Stall propagation in a processing system with interspersed processors and communicaton elements

ABSTRACT

A processing system includes processors and dynamically configurable communication elements (DCCs) coupled together in an interspersed arrangement. A source device may transfer a data item through an intermediate subset of the DCCs to a destination device. The source and destination devices may each correspond to different processors, DCCs, or input/output devices, or mixed combinations of these. In response to detecting a stall after the source device begins transfer of the data item to the destination device and prior to receipt of all of the data item at the destination device, a stalling device is operable to propagate stalling information through one or more of the intermediate subset towards the source device. In response to receiving the stalling information, at least one of the intermediate subset is operable to buffer all or part of the data item.

CONTINUATION DATA

This application is a continuation of U.S. application Ser. No.12/781,422, titled “Processing System With Interspersed Processors UsingSelective Data Transfer Through Communication Elements,” filed May 17,2010, which is a continuation of U.S. application Ser. No. 12/028,565,now U.S. Pat. No. 7,937,558, titled “Processing System with InterspersedProcessors and Communication Elements,” filed on Feb. 8, 2008, which isa continuation of U.S. patent application Ser. No. 10/602,292, now U.S.Pat. No. 7,415,594, titled “Processing System With Interspersed StallPropagating Processors And Communication Elements,” filed on Jun. 24,2003, and which claims benefit of priority of provisional applicationSer. No. 60/391,734 titled “Mathematical Matrix Algorithm Processor”filed on Jun. 26, 2002, all of which are incorporated herein byreference in their entirety as though fully and completely set forthherein.

FIELD OF THE INVENTION

This invention relates to computer systems, and more particularly, toparallel processor systems.

DESCRIPTION OF THE RELATED ART

The need for parallel computation arises from the need to processmultiple complex signals at high speed, in applications such as radar,sonar, video, cinema, medical imaging, and telecommunications. Parallelcomputation also may provide greater computational throughput and mayovercome certain limitations of the serial computation approach. Thecapability of a system may be described by metrics of performance for agiven cost or physical size. Initially the only computer performancemetric of interest was calculations per second. With the increasing useof battery-powered equipment, computational performance per energy unitis more often the preferred metric.

Conventional approaches to achieving high performance computation are:

-   -   1. General-purpose microcomputers (GPMCs). GPMCs (such as the        Pentium line from Intel, and the PowerPC series from Motorola        and IBM) have been adapted to maximize throughput at the expense        of latency. Latency is the delay through the GPMC chip between        input and output data for a single operation. Latency is long        because the data is grouped with other data going into and out        of the chip, and the operation is embedded in a pipeline with        many stages of other operations. Almost all computers have a        memory hierarchy; for example, a small amount of fast SRAM        registers at the top of the hierarchy, a moderate amount of        slower system memory in the middle of the hierarchy, and a large        amount of very slow disk-drive-based storage at the bottom. In        GPMCs each processor may have a register file for data, an        instruction issue unit, and a level-one (L1) cache. The L1 cache        may be split between instructions and data or may be unified.        Caches improve performance because of the locality of references        in most computer programs, i.e., the tendency of the next        operation to reference a memory location nearby the        last-referenced memory location. A level-2 (L2) cache is usually        needed to interface with main memory (larger, slower, cheaper        dynamic RAM chips). Many GPMC chips support        single-instruction-multiple-data (SIMD) parallelism through        several execution units; some of the largest chips support        multiple instruction streams for MIMD behavior. In a GPMC with        multiple execution units, the L2 cache is usually shared among        execution units, with some “cache-coherence” scheme to prevent        loss of data when writing to this shared memory. An L3 cache may        be used if the main memory is relatively much slower. Additional        controllers for memory and I/O channels may be integrated on the        same chip. The general-purpose programmability and large market        for GPMCs allows them to be mass-produced and sold at low unit        cost. The disadvantages of the GPMC and its complex of caches        and pipelines include relatively high power dissipation and the        aforementioned relatively large latencies from when data enters        the CPU to when results are output.    -   2. Digital signal processors (DSPs). DSPs may be divided into        classes according to whether the ALU uses fixed-point or        floating-point numbers, and also by the number of ALUs per IC        chip. Power dissipation per operation is usually less for DSPs        than GPMCs due to the use of specialized instructions to        facilitate signal processing. DSPs may exhibit less latency than        GPMCs for a given operation due to fewer cache layers and        shorter pipelines. Instruction words may be longer, permitting        explicit parallel execution, compared to automatic/speculative        parallel execution in the GPMCs. Higher performance DSP        implementations may support parallelism through multiple        execution units, and in general, DSPs require fewer support        chips than GPMCs. The large market for DSPs allows them to be        mass-produced at low cost. In the DSP market there is demand for        ICs that perform fixed-point arithmetic only, as well as for ICs        that support both fixed- and floating-point operations. The        disadvantages of DSPs include greater difficulty of programming,        and poorer performance on certain types of algorithms.    -   3. Field-programmable gate arrays (FPGAs). FPGAs are digital        ICs, which can be programmed or customized by users “in the        field” as opposed to during wafer fabrication. FPGAs may be        classified by the number of logic gates they contain, and in the        more recent, largest versions, by the number of ALUs and memory        on the IC. Theoretically all the FPGA ALUs can compute in        parallel, following a SIMD or MIMD or mixed control paradigm.        Customizing an FPGA is similar to programming a DSP/GPMC, but        arriving at the desired program is more difficult, generally        requiring engineers who are knowledgeable in logic design, and        specialized design automation tools. However, if speed is more        important than power dissipation, FPGAs often provide faster        processing than DSP/GPMCs. Although mass-produced, large FPGAs        are several times more expensive than GPMC chips with the same        number of gates.    -   4. Application specific integrated circuits (ASICs). ASICs are        customized to specific applications by designing specific        circuit layouts which may range from full custom circuits to        hierarchical integration of library modules. Library modules may        range from individual logic gates and I/O cells to memory arrays        and microprocessor cores. Performance can be higher than        GPMC/DSP/FPGA approaches because the ASIC hardware is tailored        to the algorithms required by the application. Speed can also be        faster than a FPGA because the configuration circuits can be        eliminated, resulting in a more compact layout with lower        parasitic capacitances. The development costs for an ASIC are        much higher than any other approach, running from several to        tens of millions of dollars (and higher for complex video        chips). Millions of chips of a particular design may need to be        sold to amortize the high costs of developing one.

A parallel processor computer considered in the abstract may be composedof processors, memories, and interconnecting networks (IN). Thesecomponents have been combined in many different topologies, described inthe literature on parallel-processor computing. All of these componentshave latency due to internal delays, and these latencies grow with thesize of the component and number of input/output ports on it. Theaverage latencies of the IN and memories grow as more and moreprocessors and memories are added to the system.

In many parallel processor arrays there is a large memory, which isshared amongst several processors by means of an interconnectionnetwork. For performance reasons the shared memory is typically similarto the L2 cache of stand-alone processor systems. The next level higher(i.e., faster) cache, or L1 cache, is often private and local to eachprocessor of the parallel array. Then within a processor there isusually a register file for data and a separate cache for instructions.There are several problems with this parallel architecture when two ormore processors are working the same task. To communicate a large vectorof data one processor must write through the L1 cache to the L2 cache,and then set a flag (also in the L2 cache). The second processor mustcontinuously read the flag until it detects that the value has beenchanged and then read the data vector into the L1 cache to work on it.Thus for newly computed results the communication rate is set by thespeed of the L2 cache, which declines as L2's capacity is made bigger toaccommodate more processors. Both bandwidth and latency of the L2 cacheare adversely affected by increased capacity.

An interconnection network may be either fully-connected or switched. Ina fully-connected network, all input ports are hardwired to all outputports. However, the number of wires in fully-connected network increasesas N²/2 where N is the number of ports, and thus a fully-connectednetwork quickly becomes impractical for even medium sized systems.

A switched network is composed of links and switching nodes. The linksmay comprise wiring, transmission lines, waveguides (including opticalwaveguides), or wireless receiver-transmitter pairs. Switching nodes maybe as simple as a connection to a bus during a time window, or ascomplex as a cross bar with many ports and buffer queues. A single-stagenetwork is one where all the input ports and output ports reside on onelarge switching node. A multi-stage network is one in which a data-movemust traverse a first switching node, a first link, a second switchingnode, and possibly more link-node pairs to get to an output port. Forexample, the telephone system is a multistage network.

Interconnection networks for parallel computers vary widely in size,bandwidth, and method of control. If the network provides a data-path orcircuit from input to output and leaves it alone until requested to tearit down, then it may be said to be “circuit-switched”. If the networkprovides a path only long enough to deliver a packet of data from inputto output, then it may be said to be “packet switched”. Control methodsvary from completely deterministic (which may be achieved by programmingevery step synchronous to a master clock) to completely reactionary(which may be achieved by responding asynchronously to data-moverequests at the port inputs).

For a single stage network the request/grant protocol is a common way tocontrol the switches. A request signal is presented to an input port andcompared to request signals from all other input ports in a contentiondetection circuit. If there is no contention the IN responds with agrant signal. The port sends an address and the IN sets switches toconnect input with output. If contention is detected then an arbitrationcircuit (or “arbiter”) will decide which one of the requesting portsgets a grant signal. Ports without a grant signal will have to wait.Ports that did not succeed in one cycle may try again in subsequentcycles. Various priority/rotation schemes are used in the arbiter toensure that every port gets at least some service.

For a multi-stage network a particular protocol called “wormholerouting” may be used. Wormhole routing is based on the idea that amessage can be formed into a chain of words with a header fornavigation, a body to carry the payload data, and a tail to close downthe path. The message “worms” its way through a network as follows.Presume a network laid out as a Cartesian grid; and that a switchingnode and a memory is located at each junction of the grid. The headercontains a sequence of simple steering directions (such asgo-straight-ahead, turn-left, turn-right, or connect-to-local memory),which indicate where the worm should go at each node it encounters inthe network. These steering directions are so simple that a node candecode them and set switches very rapidly with little circuitry. Thepath, or “hole”, set up by the header allows the passage of the payloaddata, the “body”, until a codeword “tail” is encountered which causesthe node to close the hole after it. Closing the path may free up linksand nodes for other paths to be created by the same wormhole routingprotocol. The bandwidth of an IN may be defined as the number ofsuccessful data moves that occur per unit time. The bandwidth of aswitched IN is hard to estimate because it depends on many factors inthe details of the IN and in the characteristics of data-move requestsput to it. Measurements and simulations show that, as the rate ofdata-move requests increases, the fraction of data-moves that actuallymake it through the IN decreases. Eventually the number of completeddata-moves per second will saturate or peak and this is taken as theIN's bandwidth.

The above systems provide varying levels of performance for differentapplications. However, certain applications require a much greater levelof performance or computational throughput than is possible usingcurrent systems. Therefore, a system is desired which offers increasedcomputational throughput while also providing reduced powerrequirements.

SUMMARY OF THE INVENTION

Various embodiments of a processing system are disclosed. In oneembodiment, the system may include a plurality of processors and aplurality of dynamically configurable communication elements. Each ofthe processors may comprise at least one arithmetic logic unit, aninstruction processing unit, and a plurality of processor ports. Eachdynamically configurable communication element may comprise a pluralityof communication ports, a first memory, and a routing engine. Theplurality of processors and the plurality of dynamically configurablecommunication elements may be coupled together in an interspersedarrangement. In one embodiment, for each of the processors, theplurality of processor ports may be configured for coupling to a firstsubset of the plurality of dynamically configurable communicationelements. Also, for each of the dynamically configurable communicationelements, the plurality of communication ports may comprise a firstsubset of communication ports configured for coupling to a subset of theplurality of processors and a second subset of communication portsconfigured for coupling to a second subset of the plurality ofdynamically configurable communication elements. In one embodiment, theplurality of processors and the plurality of dynamically configurablecommunication elements may be manufactured on a single integratedcircuit.

In one specific implementation, each of the processors may be coupled toeach of a plurality of neighboring dynamically configurablecommunication elements via a respective one of the plurality ofprocessor ports. Each of the dynamically configurable communicationelements may be coupled to a plurality of neighboring processors via arespective one of the first subset of the plurality of communicationports, and may be coupled to each of a plurality of neighboringdynamically configurable communication elements via a respective one ofthe second subset of the plurality of communication ports.

In one embodiment, one of the processors may be configurable as a sourcedevice to transfer a first plurality of data through an intermediatesubset of the plurality of dynamically configurable communicationelements to a destination device. After the source device begins thetransfer, if either the destination device or one element of theintermediate subset stalls, the stalling device may be operable topropagate stalling information through one or more elements of theintermediate subset to the source device. The source device may beoperable to suspend transfer of the first plurality of data upon receiptof the stalling information, and a portion of the first plurality ofdata transmitted after stalling and prior to suspension may be bufferedin at least one element of the intermediate subset. Alternatively, afterthe source device begins transfer of the first plurality of data throughthe intermediate subset to the destination device, if either the sourcedevice or one element of the intermediate subset stalls, the stallingdevice may be operable to propagate stalling information through one ormore elements of the intermediate subset to the destination device. Thedestination device may be operable to suspend processing of the firstplurality of data upon receipt of the stalling information.

In one embodiment, each of the dynamically configurable communicationelements may comprise a plurality of input ports, a plurality of outputregisters, and a crossbar coupled to receive data from one or more ofthe plurality of input ports and to transmit data to a selected one ormore of the plurality of output registers. Each output register mayselectively operate in a synchronous data transfer mode or a transparentdata transfer mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one embodiment of a processingsystem, referred to herein as a mathematical matrix algorithm processor(MMAP).

FIG. 2 is a block diagram illustrating one embodiment of a MMAPconnection scheme.

FIG. 3 is a block diagram illustrating one embodiment of a processor,also called a dynamically configurable processor (DCP).

FIG. 4 is a block diagram illustrating one embodiment of a dynamicallyconfigurable communication element (DCC).

FIG. 5 is a timing diagram illustrating one embodiment of an assignmentof memory access types to a clock cycle.

FIG. 6 is a timing diagram illustrating the operation of one embodimentof a synchronous data transmission mode.

FIG. 7 is a timing diagram illustrating the operation of severalembodiments of a transparent data transmission mode.

FIG. 8 is a flow diagram illustrating the operation of one embodiment ofconfigurable mode data transmission in a MMAP.

FIG. 9 is a flow diagram illustrating the operation of one embodiment offlow control in a MMAP.

FIG. 10 is a diagram illustrating the operation of one embodiment ofrouting logic on a header word.

FIG. 11 is a block diagram illustrating an example pathway through aportion of a MMAP.

FIG. 12 is a flow diagram illustrating data flow in one embodiment of abutterfly calculation.

FIG. 13 is a block diagram of a portion of a MMAP embodimentillustrating data sharing.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION

FIG. 1—MMAP Block Diagram and Overview

FIG. 1 is a block diagram illustrating one embodiment of a processingsystem. In the present description, the processing system is referred toas a mathematical matrix algorithm processor (MMAP), although use ofthis name is not intended to limit the scope of the invention in anyway. In the illustrated embodiment, MMAP 10 includes a plurality ofdynamically configurable processors (DCPs) and a plurality ofdynamically configurable communicators (DCCs), also called “dynamicallyconfigurable communication elements”, coupled to communicate data andinstructions with each other. As used herein, a DCP may also be referredto as a DCP node, and a DCC may also be referred to as a DCC node.

The processing system 10 may be used in any of various systems andapplications where GPMCs, DSPs, FPGAs, or ASICs are currently used.Thus, for example, the processing system 10 may be used in any ofvarious types of computer systems or other devices that requirecomputation. In one contemplated embodiment, the processing system 10 isused as a signal processing device in a digital television system, astaught in U.S. provisional patent application Ser. No. 60/396,819 titled“Frequency Domain Equalization Algorithm” filed on Jul. 18, 2002, whichis hereby incorporated by reference.

In one embodiment, a DCP may include one or more arithmetic-logic units(ALUs) configured for manipulating data, one or more instructionprocessing units (IPUs) configured for controlling the ALUs, one or morememories configured to hold instructions or data, and multiplexers anddecoders of various sorts. Such an embodiment may include a number ofports (“processor ports”), some of which may be configured forconnection to DCCs and others that may be configured for connection toother DCPs. FIG. 3 is a block diagram of one embodiment of a DCP, and isdescribed further below.

In one embodiment, a DCC may include one or more random access memories(RAMs) configured to hold data and instructions, a configurablecontroller, a network switch such as a crossbar switch, registers, andmultiplexers. Such an embodiment may include a plurality of ports, someof which may be configured for connection to DCPs (referred to herein asDCP-type ports) and others that may be configured to connect to DCCs(referred to herein as DCC-type ports). FIG. 4 is a block diagram of oneembodiment of a DCC, and is described further below. It is noted thatfor any given port, whether configured for connection to or from a DCCor DCP, the amount of data transferable through such a given port in aparticular clock cycle may vary in various embodiments. For example, inone embodiment, a given port may be configured to transfer one word ofdata per clock cycle, whereas in another embodiment a given port may beconfigured to transfer multiple words of data per clock cycle. In yetanother embodiment, a given port may employ a technique such astime-division multiplexing to transfer one word of data over multipleclock cycles, thereby reducing the number of physical connectionscomprising the port.

In one embodiment of MMAP 10, each DCP may include a small local memoryreserved for instructions and may include very little local datastorage. In such an embodiment, DCCs neighboring each DCP may beconfigured to provide operands to a given DCP. In a particularembodiment, for many DCP instructions a given DCP may read operands fromneighboring DCCs, execute an ALU operation, and store an ALU result to agiven neighboring DCC in one clock cycle. An ALU result from one DCP maythereby be made available to several other DCPs in the clock cycleimmediately following execution. Producing results in this fashion mayenable the execution of neighboring DCPs to be closely coordinated or“tightly coupled.” Such coordination is referred to herein ascooperative processing.

As used herein, from the perspective of a given DCC or DCP, aneighboring DCC or DCP refers to a DCC or DCP that can be accessed fromthe given DCC or DCP within a particular latency. In some embodiments,the latency defining the extent of a neighboring relationship may varydepending on factors such as clock speed, for example. Further, in someembodiments, multiple degrees of neighboring may be defined, whichdegrees may correspond to different access latencies. For example, inone embodiment, a “nearest neighbor” may be defined as a device that cansupply data during the same clock cycle during which it is requested, a“next-nearest neighbor may be defined as a device that can supply datawithin one clock cycle after it is requested, and so forth. In otherembodiments, it is contemplated that other metrics may be used toquantify a neighboring relation.

In a given MMAP embodiment, some DCCs and DCPs may be logically adjacentto other DCCs and DCPs. As used herein, “logically adjacent” refers to arelation between two devices, such as one DCC and another DCC, or oneDCC and one DCP, such that one or more ports of one device are directlyconnected to respective ports of the other device without passingthrough an intervening DCC or DCP. Further, in a given MMAP embodiment,some DCCs and DCPs may be physically adjacent to other DCCs and DCPs. Asused herein, “physically adjacent” refers to a relation between twodevices, such as one DCC and another DCC, or one DCC and one DCP, suchthat no other DCC or DCP is physically located between the two devices.

In some MMAP embodiments, devices such as DCCs and DCPs that arelogically and/or physically adjacent are also neighboring or neighbordevices. However, it is noted that in some embodiments, logical and/orphysical adjacency between given devices does not entail a neighboringrelation, or a particular degree of neighboring relation, between thegiven devices. For example, in one embodiment one DCC may be directlyconnected to another DCC that is located a considerable distance away.Such a pair may be logically adjacent but not physically adjacent, andthe signal propagation time from the one DCC to the other may be toogreat to satisfy the latency requirement of neighbors. Similarly, in oneembodiment one DCC may be physically adjacent to another DCC but notdirectly connected to it, and therefore not logically adjacent to it.Access from the one DCC to the other DCC may traverse one or moreintermediate nodes, and the resulting transit delay may be too great tosatisfy the latency requirement of neighbors.

Depending on the technology and implementation of a given embodiment ofMMAP 10, the specific number of the DCC's plurality of ports as well asthe size of the DCC RAM may be balanced against the overall desiredexecution speed and size of the DCC. For example, one DCC embodiment mayinclude 4 DCP-type ports, 4 DCC-type ports, and 4K words of memory. Sucha DCC embodiment may be configured to provide a direct memory access(DMA) mechanism. A DMA mechanism may allow a given DCC to copy dataefficiently to or from other DCCs, or to or from locations external toMMAP 10, while DCPs are computing results.

In one embodiment of MMAP 10, data and instructions may be transferredamong the DCCs in one of several different ways. A serial bus may beprovided to all memories in MMAP 10; such a bus may be used toinitialize MMAP 10 from external memory or to support testing of MMAPdata structures. For short-distance transfers, a given DCP may beprogrammed to directly move data to or from its neighbor DCCs. Totransfer data or instructions over longer distances, communicationpathways may be dynamically created and destroyed in the network ofDCCs.

For the purpose of such longer-distance data transfer, a network ofinterconnected DCCs within MMAP 10 may constitute a switched routingfabric (SRF) for communication pathways. In such an embodiment, theremay be at least two methods for managing communication pathways in theSRF. A first method is by global programming, wherein paths may beselected by software control (for example, either by a human programmeror by a compiler with a routing capability) and instructions may becoded into DCC configuration controllers to program the crossbarappropriately. To create a pathway, every DCC along the pathway may beexplicitly programmed with a particular routing function. In a dynamicenvironment where pathways are frequently created and destroyed, a largenumber of crossbar configuration codes may be required, storage of whichmay in turn consume potentially limited DCC RAM resources.

A second method for managing communication pathways is referred to as“wormhole routing”. To implement wormhole routing, each DCC may includea set of steering functions and a mechanism to stop and restart theprogress of a sequence of words, referred to as a worm, through the SRF.Because the steering functions may be commonly used and re-used by allcommunication pathways, the amount of configuration code that may occupyDCC RAM may be much smaller than for the global programming methoddescribed above. For the wormhole routing method, software control maystill be used to select the particular links to be used by a pathway,but the processes of pathway creation (also referred to herein as setup) and destruction/link release (also referred to herein as teardown)may be implemented in hardware with minimal software intervention.

To prevent potential loss of data words on a pathway, an embodiment ofMMAP 10 may implement flow control between receivers and transmittersalong the pathway. Flow control refers to a mechanism that may stop atransmitter if its corresponding receiver can no longer receive data,and may restart a transmitter when its corresponding receiver becomesready to receive data. Because stopping and restarting the flow of dataon a pathway has many similarities to stopping and restarting theprogress of a worm in wormhole routing, the two may be combined in anintegrated scheme.

In one embodiment, MMAP 10 may include pluralities of DCPs and DCCs,which DCPs may be identical and which DCCs may be identical, connectedtogether in a uniform array. In a uniform array, the majority of DCPsmay be identical and each of a majority of DCPs may have the same numberof connections to DCCs. Also, in a uniform array, the majority of DCCsmay be identical and each of a majority of DCCs may have the same numberof connections to other DCCs and to DCPs. The DCPs and DCCs in one MMAPembodiment may be interspersed in a substantially homogeneous fashion.As used herein, a substantially homogeneous interspersion refers to anarrangement in which the ratio of DCPs to DCCs is consistent across amajority of subregions of an array.

A uniform array arranged in a substantially homogeneous fashion may havecertain advantageous characteristics, such as providing a predictableinterconnection pattern and enabling software modules to be re-usedacross the array. In one embodiment, a uniform array may enable a smallnumber of instances of DCPs and DCCs to be designed and tested. A systemmay then be assembled by fabricating a unit comprising a DCC and a DCPand then repeating or “tiling” such a unit multiple times. Such anapproach may lower design and test costs through reuse of common systemelements.

It is also noted that the configurable nature of the DCP and DCC mayallow a great variety of non-uniform behavior to be programmed to occuron a physically uniform array. However, in an alternative embodiment,MMAP 10 may also be formed with non-uniform DCC and DCP units, which maybe connected in a regular or irregular array, or even in a random way.In one embodiment, DCP and DCC interconnections may be implemented ascircuit traces, for example on an integrated circuit (IC), ceramicsubstrate, or printed circuit board (PCB). However, in alternativeembodiments, such interconnections may be any of a variety of miniaturecommunication links, such as waveguides for electromagnetic energy(i.e., radio or optical energy), wireless (i.e., unguided) energy,particles (such as electron beams), or potentials on molecules, forexample.

The MMAP 10 may be implemented on a single integrated circuit. In oneembodiment, a plurality of MMAP integrated circuits may be combined toproduce a larger system. A given embodiment of MMAP 10 may beimplemented using silicon integrated circuit (Si-ICs) technology, andmay employ various features to account for specific characteristics ofsuch a technology. For example, the circuits on a Si-IC chip may beconfined to a thin plane. Correspondingly, a given embodiment of MMAP 10may employ a two-dimensional array of DCPs and DCCs such as thatillustrated in FIG. 1. However, alternative MMAP embodiments arecontemplated that include different arrangements of DCPs and DCCs.

Further, the available wiring density on a Si-IC chip may be much higherthan between such chips, and each chip may have a perimeter of specialInput/Output (I/O) circuits to interface on-chip signals and off-chipsignals. Correspondingly, a given embodiment of MMAP 10 may employ aslightly non-uniform array composed of a uniform array of DCPs and DCCsin core of the chip, and modified DCP/DCC units along the perimeter ofthe chip. However, alternative MMAP embodiments are contemplated thatinclude different arrangements and combinations of uniform and modifiedDCP/DCC units.

Also, computational operations performed by Si-IC circuits may produceheat, which may be removed by IC packaging. Increased IC packaging mayrequire additional space, and interconnections through and around ICpackaging may incur delays that are proportional to path length.Therefore, as noted above, very large MMAPs may be constructed byinterconnecting multiple chips. Programming of such multiple-chip MMAPembodiments may take into account that inter-chip signal delays are muchlonger than intra-chip delays.

In a given Si-IC MMAP 10 embodiment, the maximum number of DCPs and DCCsthat may be implemented on a single chip may be determined by theminiaturization possible with a given Si-IC technology and thecomplexity of each DCP and DCC. In such a MMAP embodiment, the circuitcomplexity of DCPs and DCCs may be minimized subject to achieving atarget level of computational throughput. Such minimized DCPs and DCCsmay be referred to herein as being streamlined. In one MMAP 10embodiment, the target level of throughput for a DCP may be comparableto that of the arithmetic execution units of the best digital signalprocessors (DSPs) made in the same Si-IC technology. However, other MMAPembodiments are contemplated in which alternative references for targetDCP throughput may be used.

In some embodiments, MMAP 10 may employ the best features of DSP andFPGA architectures. Like a DSP, MMAP 10 may be a programmable chip withmultiple processing units and on-chip memory. However, relative to aDSP, the MMAP processing units may be streamlined, there may be more ofthem, and they may be interconnected in a novel way to maximize thebandwidth of data movement between them as well as data movement on andoff the chip. Having more processing units than a DSP may allow MMAP 10to do more multiplications per unit time, and streamlined processingunits may minimize energy use. Many DSPs with internal parallelism maybe bus-oriented architectures. In some embodiments, MMAP 10 may notinclude a bus, but rather may include neighboring shared local memories,such as in a DCC, embedded in an SRF that may provide significantlyhigher total bandwidth than a bus-oriented architecture.

Compared to the FPGA approach, some MMAP embodiments may be morecoarsely grained. For example, in one MMAP embodiment, operations mayhave a natural word length (e.g., 16-bits) and computation may be mostefficient if performed using data that is a multiple of the natural wordlength. In some MMAP embodiments, DCPs and DCCs may be denser than theequivalent structures realized in FPGA, which may result in shorteraverage wiring length, lower wiring capacitance and less energy use. Incontrast to an FPGA implementation, in some MMAP embodiments, every ALUin the MMAP may be part of a processor (i.e., a DCP), which mayfacilitate the setup of operands and the delivery of results tosurrounding fast memory in the DCCs.

MMAP Topology and Communication

MMAP 10 illustrated in FIG. 1 may supply the DCPs with ample connectionsto fast memory by interspersing DCCs between the DCPs, as shown. Such anarrangement may reduce the time required for a given DCP to accessmemory in a DCC relative to a segregated (i.e., non-interspersed)arrangement, and may be referred to herein as an interspersed gridarrangement. In the embodiment of FIG. 1, the ratio of DCPs to DCCs is1:1. However, other MMAP embodiments are contemplated that may includedifferent ratios of DCPs to DCCs.

Connections between DCCs and DCPs are not explicitly shown in FIG. 1,because there may be many possible connection schemes. Several possibleconnection schemes for a given MMAP embodiment may include:

-   -   1. PlanarA—In this scheme each DCP may connect to its four        neighbor DCCs via DCP-type ports on each such neighbor DCC.        Also, each DCC may connect to its four neighbor DCCs via        DCC-type ports on each such neighbor DCC. Each connection type        may be composed of a set of parallel circuit traces or wires. In        a uniform array, the number of wires in a connection type may be        uniform across the array.    -   2. PlanarB—This scheme is the same as the PlanarA scheme except        that additional connections may be made between DCCs and DCPs        with a serial bus for the purpose of loading an initial state        from a serial memory.    -   3. PlanarC—This scheme is the same as PlanarB except that        additional parallel connections may be made between DCCs        separated by many rows and columns of the array. Such additional        connections may boost the bandwidth and reduce the latency        between the more distant DCCs.    -   4. PlanarD—This scheme is a subset of PlanarC such that the        additional connections may represent the edges of a hypercube        where each DCC is a vertex of the same hypercube.    -   5. PlanarE—This scheme is a subset of PlanarC such that the        additional connections may be made to a second chip bonded to        the first with many connections so that the two arrays may be        tightly coupled.    -   6. StackedA—This scheme is a subset of Planar C such that the        additional connections may support a three dimensional matrix.

It is noted that additional connection schemes are contemplated in whichDCCs and DCPs may be connected in different topologies using differenttypes and numbers of connections.

FIG. 2—MMAP Connection Scheme

FIG. 2 is a block diagram illustrating one embodiment of a MMAPconnection scheme. MMAP connection scheme 20 includes a plurality ofDCCs and DCPs and may be illustrative of a portion of the MMAP ofFIG. 1. In the MMAP connection scheme 20, each DCP is connected to fourneighbor DCCs, while each DCC is connected to four neighbor DCPs as wellas four neighbor DCCs. MMAP connection scheme 20 may therefore beillustrative of the PlanarA connection scheme discussed above.

To support high-bandwidth ports in MMAP connection scheme 20, theconnections between ports (DCP-to-DCC, or DCC-to-DCC) may be short(i.e., limited to neighbors) and word-wide, meaning the number ofelectrical conductors (lines) in the data part of the connection may bethe same as the number of bits used in the ALU operands. The DCP-to-DCCconnections may include address lines. The DCC-to-DCC connections maynot necessarily have address lines but may have lines for flow control.

By keeping the DCP nodes simple, large arrays (for example, in one MMAPembodiment, 16 rows times 16 columns=256 DCPs) may be put on a singleVLSI IC at modest cost. Suitable VLSI technologies may include but arenot restricted to complementary metal-oxide semiconductor (CMOS) fieldeffect transistors with or without bipolar transistors in silicon orother semiconductors.

In some MMAP embodiments, communication between nodes may be underprogrammer control. In a MMAP each DCP may communicate data/instructionswith neighboring DCCs, and optionally on through those DCCs to otherDCCs and DCPs. For moving small blocks of data, DCPs can be usedcooperatively to move data across the array through a series oftransfers—one word at a time, per DCP. In such a method, the first DCPin the path from a source node to a destination node may read from aneighbor DCC memory during the read phase of a clock cycle and may writeto another neighbor DCC during the write phase of a clock cycle. Thesecond DCP in the path may similarly read and write data, and theprocess may continue until the data arrives at the destination node.Data may also be scaled or normalized by a given DCP as it propagatesalong the way to its destination node. Using this method, programmingmay set up bucket brigade lines and trees across the array to move datawhere it is needed. However, for longer distances and larger amounts ofdata, many moves may be required to transport data and many DCPs maytherefore spend a majority of cycles simply moving data instead ofperforming more useful arithmetic.

For longer distance block moves, some MMAP embodiments may provide meansfor memory-to-memory transfers between DCCs without involving the DCPs.A DCP may indirectly access a DCC-type port in a neighbor DCC throughspecial RAM addresses associated with such ports. This may permit a DCPto create a new pathway for sending a worm and later to tear such apathway down, or alternatively to receive a worm. A DCP may also save ablock of data to be transferred in RAM in a neighbor DCC and then directthe neighbor DCC to begin a DMA operation through special RAM addressesassociated with such operations. This may permit the DCP to proceed withother tasks while the neighbor DCC coordinates the DMA transfer of thedata.

Various embodiments of the MMAP may offer an advantageous environmentfor executing useful algorithms. Algorithms of interest (e.g., foranalyzing image data) may be broken up into flow diagrams of ALUs. Eachflow diagram may be mapped onto the MMAP array as a tree, a lattice, orany arbitrary network, including multiple feedback/feed-forward paths.The finite precision of one ALU may be expanded to obtain multi-wordprecise results by combining several DCPs and DCCs. When mapping a flowdiagram to the MMAP, communication delays between DCP/DCC nodes that areproportional to the distances between nodes may arise. Also, a mappingmay require more memory at each node if communication queues are largeor if reconfiguration is frequent. These factors may be compensated forby careful programming, which may take communication delays, queuing,and reconfiguration into account.

Systolic algorithms represent a class of algorithms that may mapparticularly efficiently to various embodiments of the MMAP. Systolicalgorithms have been developed for a variety of applications in matrixarithmetic, image processing, and signal processing. In a systolicalgorithm many processors may cooperate in a synchronized way to performa difficult computation. In an ideal algorithm implementation, eachprocessor may perform the same operation (or small loop of operations)over and over for as long as the algorithm is needed, and data may flowthrough the network of processors by neighboring connections withbalanced production and consumption of data-words. If each intermediateresult data word produced is then immediately consumed by a subsequentcalculation, then the amount of memory required may be minimized. Theadvantages of a systolic algorithm may include the ability to usestreamlined processors, to minimize memory requirements, and to achievea high arithmetic operation rate using standard, low cost VLSItechnology.

A MMAP embodiment may have many processors per chip and a MIMDarchitecture, which may be configured to emulate the operation of otherclasses of systems, such as SIMD systems and distributed MIMD systems.In some embodiments, a MMAP may run different algorithms in differentareas of the chip at the same time. Also, to save power, in someembodiments a programmer can selectively enable and disable the clock toat least some DCPs and DCCs, enabling unused DCPs and DCCs to bedisabled.

Dynamically Configurable Processor

FIG. 3 is a block diagram illustrating one embodiment of a dynamicallyconfigurable processor (DCP). DCP 300 may be illustrative of the DCPshown in FIG. 1 and FIG. 2. DCP 300 includes instruction processing unit(IPU) 310 coupled to control at least one arithmetic logic unit (ALU)320. DCP 300 also includes a plurality of data input ports 301 coupledto a plurality of multiplexers (also referred to herein as muxes), whichare in turn coupled to select at least a first and second operand inputfor ALU 320 as well as to select program load path data for instructionprocessing unit 310. DCP 300 further includes a plurality of data outputports 302 coupled via a mux to receive result data from ALU 320, as wellas a plurality of address ports 303 coupled to receive address data frominstruction processing unit 310.

Address ports 303 may be configured to convey addresses for reading andwriting RAM data contained in neighboring dynamically configurablecommunicators (DCCs). Data input ports 301 and data output ports 302 maybe configured to convey data from and to neighboring DCCs. In asynchronous operating mode, data written via data output ports 302 to aneighboring DCC during one clock cycle may be available to be read viadata input ports 301 of a neighboring DCP 300 during the immediatelyfollowing clock cycle without additional delay or coordination overhead.

In the illustrated embodiment of DCP 300, data input ports 301, dataoutput ports 302, and address ports 303 each include four ports. Also, asingle ALU 320 is shown. However, alternative embodiments arecontemplated in which other numbers of data input ports, data outputports, or address ports are provided, and in which different numbers ofALUs may be included. In a MMAP embodiment including multiple instancesof DCP 300 in a rectangular array, such as the MMAP embodimentillustrated in FIG. 1, the various ports may be evenly distributedaround the four sides of each DCP node.

DCP 300 may be configured to perform arithmetic/logical unit operationson data words, where the selected operation depends on the currentinstruction being processed by IPU 310. To support flexible programming,IPU 310 may include at least one instruction memory 312 including aplurality of addressable locations, instruction decoder 314, and addressgenerator 316, each interconnected via a variety of interconnectmechanisms. In other embodiments, it is contemplated that IPU 310 maycontain more than one instruction memory or may contain additionalfunctionality. It is further contemplated that in other embodiments, thefunctionality illustrated in IPU 310 may be partitioned into differenttypes of functional units or implemented in a single functional unit.

IPU 310 may be configured to receive program data for storage ininstruction memory 312 via the program load path coupled to data inputports 301. Instruction memory 312 may also be written and read through aglobal serial bus (not shown). Depending on the decode of a particularinstruction by instruction decoder 312, IPU 310 may be configured tocontrol the various muxes coupled to data input ports 301 and dataoutput ports 302, to guide data to and from neighboring DCCs. IPU 310may further be configured to convey addresses generated by addressgenerator 316 via address ports 303 to neighboring DCCs, for example toread or write RAM located therein. Address generator 316 may alsoinclude a program counter register (not shown) configured to generate anext instruction address to be fetched from instruction memory 312 anddecoded by instruction decoder 314.

In one embodiment, DCP 300 may not include a data register file, datacache, or any local storage for data operands or result data. In such anembodiment, DCP 300 may be configured to utilize a memory included in aDCC to which DCP 300 is immediately connected as a fast storage mediumfrom which data operands may be read and to which result data may bewritten. In some embodiments, a given DCP may obtain different data fromdifferent neighbor DCCs simultaneously or at different times. Asdescribed in greater detail below, in some embodiments a given DCP mayalso be configured to read and write data in DCCs to which the given DCPis not immediately connected, by establishing a pathway from such remoteDCCs to a neighbor DCC of the given DCP.

Instructions implemented by DCP 300 may support arithmetic and logicaloperations, as well as meta-instructions. DCP instructions may be longenough in bits to address memories for two operands and one result,which may allow these values to be read and written in one clock cycle.In one embodiment, DCP 300 may implement the following instructions:

-   -   Add (operand-address, operand-address, result-address)    -   Subtract (operand-address, operand-address, result-address)    -   Multiply (operand-address, operand-address, result-address)    -   Multiply and Add to last Result (operand-address,        result-address)    -   Multiply and Subtract from last Result (operand-address,        result-address)    -   Negate a number (type, operand-address, result-address)    -   Absolute value of a number (type, operand-address,        result-address)    -   Shift (type, operand-address, result-address)    -   XOR (mask-address, operand-address, result-address)    -   Invert (mask-address, operand-address, result-address)    -   Jump (condition, stride, PC-destination)    -   Repeat (start, stop, stride)    -   Loop (times, PC-start-of-block)    -   Branch-on-Condition(test, destination)        -   Pre-instructions are special instructions to set indexing            registers in the address generator.    -   Store-index (indexname, value)    -   Stride-index (indexname, value)

It is noted that other embodiments are contemplated in which DCP 300 mayimplement additional instructions, or a different set of instructions.In some embodiments, during execution of a given instruction requiringone or more data operands, a given DCP may be configured to directlyaccess memory in a neighboring DCC to access the required operands.

DCP 300 may be configured to execute meta-instructions. As used herein,a meta-instruction refers to an instruction that may perform anoperation on instructions stored in DCP instruction memory, such asinstruction memory 312. A basic meta-instruction may be to loadinstruction memory 312 from RAM in a neighboring DCC (i.e., to load anoverlay). By loading instruction memory from DCC memory, thepartitioning of memory between data and instructions may be determinedby software programming. Therefore an application programmer mayoptimize his software for best utilization of the available memory. Insome embodiments, DCP 300 may include other meta-instructions that maymodify IPU instruction memory, or save instruction memory in DCC memoryfor test, error analysis, and/or error recovery, for example.

ALU 320 may be configured to perform arithmetic for at least afixed-point number system, including the operations defined by theinstructions supported in a particular DCP 300 embodiment. For example,in one embodiment, ALU 320 may be configured to perform fixed-point add,subtract, multiply, multiply-accumulate, logical, and shift operations.In some embodiments, ALU 320 may be configured to retain the carry bitresulting from a previous computation, for supporting extended precisionarithmetic. In other embodiments, ALU 320 may be configured to performfloating point arithmetic or special-purpose operations chosen forimplementing a particular algorithm.

Dynamically Configurable Communicator

FIG. 4 is a block diagram illustrating one embodiment of a dynamicallyconfigurable communicator (DCC). It is noted that the terms “dynamicallyconfigurable communicator” and “dynamically configurable communicationelement” may be used interchangeably herein. DCC 400 may be illustrativeof the DCC shown in FIG. 1 and FIG. 2. DCC 400 includes a plurality ofDCP input ports 401 coupled to multi-port static RAM (SRAM) 425 via aplurality of muxes coupled to SRAM control 415. Multi-port SRAM 425 iscoupled to a plurality of address decoders 420 as well as to SRAMcontrol 415 and a plurality of DCP output ports 402. Address decoders420 are coupled to receive SRAM addresses via a plurality of muxescoupled to a plurality of DCC port decoders 410 and to SRAM control 415.DCC port decoders 410 are coupled to receive SRAM addresses from aplurality of DCP address ports 403.

DCC 400 further includes a plurality of DCC input ports 404 coupled tocrossbar 450 and routing logic 435 via a plurality of muxes and aplurality of input registers 454. Crossbar 450 is coupled to routinglogic 435, which is in turn coupled to communication controller 430.Communication controller 430 is coupled to address decoders 420 via aplurality of muxes and to multi-port SRAM 425 via a program load path.Crossbar 450 is further coupled to a plurality of DCC output ports 405via a plurality of output registers 455.

Output registers 455 are coupled to multi-port SRAM 425 via a pluralityof muxes. DCP input ports 401 and multi-port SRAM 425 are each coupledto crossbar 450 via a plurality of muxes coupled to routing logic 435and by input registers 454. Routing logic 435 is also coupled to DCCport decoders 410 and output registers 455.

DCP input ports 401 and DCP output ports 402 may be respectivelyconfigured to receive data from and send data to neighboring DCPs of DCC400. DCP address ports 403 may be configured to receive addresses fromneighboring DCPs of DCC 400. DCC input ports 404 and DCC output ports405 may be respectively configured to receive data from and send data toneighboring DCCs of DCC 400. In the illustrated embodiment of DCC 400,DCP input ports 401, DCP output ports 402, address ports 403, DCC inputports 404, and DCC output ports 405 each include four ports. However,alternative embodiments are contemplated in which other numbers of DCPinput ports, DCP output ports, address ports, DCC input ports, or DCCoutput ports are provided.

Multi-port SRAM 425 may include a plurality of addressable locations andmay be configured to provide high-bandwidth data transfer to neighborDCPs. Multi-port SRAM 425 may thereby effectively serve as a sharedregister file for each of the neighbor DCPs coupled to DCC 400.Multi-port SRAM 425 may further be configured to support multipleconcurrent read and write accesses via a plurality of read, write, andaddress ports. In one particular embodiment, multi-port SRAM 425 may beconfigured to substantially simultaneously provide a plurality of valuesstored in a plurality of addressable locations to a plurality ofneighbor DCPs, and to substantially simultaneously write a plurality ofvalues received from a plurality of neighbor DCPs to a plurality ofaddressable locations.

Address decoders 420 may be configured to decode an address of a givenaccess into a format suitable for interfacing with multi-port SRAM 425at a high speed, such as a fully decoded row and column address, forexample. SRAM control 415 may be configured to control the behavior ofmulti-port SRAM 425 during reads and writes, such as by enablingappropriate read and write ports, for example. SRAM control 415 may alsobe configured to control the source of addresses and data presented tomulti-port SRAM 425. For a given address port of multi-port SRAM 425,SRAM control 415 may direct address decoders 420 to use either anaddress supplied by address ports 403 via DCC port decoders 410 or anaddress supplied by communication controller 430. Similarly, for a givenwrite port of multi-port SRAM 425, SRAM control 415 may directmulti-port SRAM 425 to select write data either from DCP input ports 401or from output registers 455.

In the illustrated embodiment, DCC 400 includes a single multi-port SRAM425. In other embodiments, it is contemplated that more than onemulti-port SRAM may be provided, and further that memory technologiesother than static RAM may be employed. In various embodiments, themulti-port SRAM functionality may be provided using any of a number ofmemory structure organizations. For example, in one embodiment, multiplebanks of memory may be employed, wherein each bank may include one ormore ports. In another embodiment, multiple SRAM memories may beemployed in the DCC, wherein each SRAM may have a different number ofports. In one embodiment, DCC 400 may also include a low bandwidthserial port (not shown) that may be configured to load or unloadmulti-port SRAM 425. Such a serial port may be useful for boot-loaders,testing, and for debugging, for example.

Crossbar 450 may include a plurality of input ports and a plurality ofoutput ports, and may be configured to route data from any input port toany one or more output ports. The specific data routing performed bycrossbar 450 may depend on the state of its included crossbarconfiguration register (CCR) 451, which may be programmed by routinglogic 435 according to a particular routing function in effect at agiven time. Communication controller 430 may be configured to programrouting logic 435 to implement a particular routing function. Thefunctions of communication controller 430 and routing logic 435 maycollectively be referred to herein as a routing engine. Implementing arouting engine hierarchically, such as in the illustrated embodiment,may allow routing functions performed by routing logic 435 to operatequickly (e.g., within a fraction of a clock cycle) while communicationscontroller 430 may provide flexibility to change routing parametersacross multiple clock cycles.

In one embodiment, CCR 451 may be divided into groups of bits, one groupper output port of crossbar 450. The number of bits in a group may be atleast sufficient to select one of the crossbar input ports. If theselected output register 450 goes through a multiplexer (e.g., to selectamong multiple DCC links) then additional bits per group may be requiredto configure the multiplexer (i.e., to select a particular link). Atleast one additional bit per group may be provided to set thetransparency of output registers 455. As described further below inconjunction with the description of FIG. 7, transparency of outputregisters 455 may be controlled by an output latch signal conveyed fromrouting logic 435 to output registers 455 and may be used to reduce thedelay for data words to propagate through DCC 400. Also, as describedfurther below in conjunction with the description of FIG. 9,transparency of input registers 454 may be controlled by an input latchsignal conveyed from routing logic 435 to input registers 454 and may beused to provide a method for flow control in a MMAP. In one embodiment,CCR 451 may contain one transparency bit for each output register 455.In such an embodiment, CCR 451 may map each output register 455 to arespective one of input registers 454, and the transparency state ofeach output register 455 may be associated with its respective inputregister 454.

CCR 451 may be updated as often as every phase of a clock cycle. CCR 451may be deterministically programmed through communications controller430, which is coupled to multi-port SRAM 425 through a program loadpath. Alternatively, programming of CCR 451 may be determined by specialcontrol words arriving through DCC input ports 404, which are coupled torouting logic 435. The control words may be interpreted by routing logic435, which may also provide them to communications controller 430.

Communication controller 430 may direct crossbar 450 to route data fromone or more of DCC input ports 404 to one or more of DCC output ports405, and may thereby relay data along a path through a MMAP array. DCC400 may provide additional communications paths for data. In theillustrated embodiment, multi-port SRAM 425 may receive data at itswrite ports from either DCP input ports 401 or output registers 455 viaa plurality of muxes or multiplexers. The multiplexers may allowcommunication controller 430 to access multi-port SRAM 425 during timeswhen multi-port SRAM 425 might otherwise be idle. Communicationcontroller 430 may be programmed to direct data to be sent frommulti-port SRAM 425 to one of DCC output ports 402, or to direct dataread from one of DCC input ports 404 to be routed through crossbar 450and written into multi-port SRAM 425 in a manner analogous to a directmemory access (DMA) feature of a general purpose microcomputer (GPMC).The program load path may allow communication controller 430 todynamically load program overlays from multi-port SRAM 425 intoinstruction RAM (not shown) internal to communication controller 430.

Additionally, in the illustrated embodiment, DCC port decoders 410 maybe used to detect that a DCP has written a DCC output port accessrequest to routing logic 435. If one of DCC output ports 405 is thusrequested, routing logic 435 may direct the data word received from therequesting DCP via DCP input ports 401 to crossbar 450 via a pluralityof multiplexers. This function may allow a given DCP to send data toother DCCs via DCC output ports 405 without first storing the data wordsin multi-port SRAM 425.

MMAP Clocking

In some embodiments, a MMAP may include a master clock, which may bedistributed to every DCP and DCC node in the MMAP array. Use of themaster clock in a given DCP or DCC node may be configurable by the MMAPprogrammer. The master clock may be used in a conventional way as acommon reference for synchronous data transfer and to sequence nodeoperation. Synchronous data transfer may be an advantageous operatingmode in that it may allow the programmer to ignore the details of signalpropagation timing. Synchronous data transfer may require that the clockperiod of the master clock be long enough that all signals may reachtheir destinations within acceptable rise and fall time limits and noisemargins to ensure correct circuit operation. During the design and testof a MMAP circuit, the longest signal delays within the circuit may bedetermined, thereby determining the highest clock frequency at which thecircuit will operate reliably.

In one MMAP embodiment, the usage of master clock by each DCP or DCCnode may be determined by each node's individual configuration asspecified in a clock-control register (not shown). Such a clock-controlregister may reside in the instruction processing unit of a DCP node,and may be written by a special instruction. One basic clockconfiguration choice may be to conserve power consumption by turning offthe clock to those DCPs and DCCs that are not used during the executionof a particular software program. Also, portions of the DCC may beconfigured to operate with registers set in transparent mode and so mayoperate without a clock. In some MMAP embodiments, it may be possible toconfigure some or all of the nodes on a chip to behave like purecombinatorial logic. In such an embodiment, to save power, a softwareprogram may be configured to turn off the master clock after all of thenodes have been initialized. This mode of programming and operation maybe FPGA-like, and may require that the programmer apply additionaleffort to ensure against data loss, races, and stuck-halted states, forexample.

In a synchronous MMAP operating mode, data transfers into and out of theDCP and DCC may be synchronous with the master clock cycle, which mayalso be referred to herein as a clock cycle. The clock cycle may beorganized into a number of phases. In one embodiment, the clock cyclemay be organized into four phases, and may thereby simplify the memoryaccess control logic for multi-port SRAM 425 in DCC 400. Multi-port SRAM425 may provide for four types of memory access denoted DCP read, DCPwrite, DCC read, and DCC write. The DCC read and write may pass datathrough crossbar 450, so they may be denoted X-bar read and X-bar write,respectively. Streamlined control may be achieved if only one memoryaccess type is assigned to each phase. It is noted that in otherembodiments, it is contemplated that different numbers and types ofmemory accesses may be used, the clock cycle may be organized into adifferent number of phases, or more than one memory access type may beassigned to a given phase. It is further contemplated that in otherembodiments, more than one master clock signal may be provided, and eachsuch master clock signal may be organized into different phases, whichmay be associated with different functions.

FIG. 5—Timing Diagram of Assignment of Memory Access Types

FIG. 5 is a timing diagram illustrating one embodiment of an assignmentof memory access types to a clock cycle. Clock cycle 500 includes foursequential phases denoted phase A through phase D, respectively.Referring collectively to FIG. 3 through FIG. 5, during clock cycle 500,DCPs such as DCP 300 may have exclusive access to memories such asmulti-port SRAM 425 during Phase A for read access only, and duringPhase D for write only. These assignments are respectively denoted “DCPread from SRAM” and “DCP write to SRAM” in FIG. 5. DCC crossbars such ascrossbar 450 may have exclusive access to memories such as multi-portSRAM 425 during Phase B for write access only and during phase C forread access only. These assignments are respectively denoted “X-BARwrite to SRAM” and “X-BAR read from SRAM” in FIG. 5. It is noted thatalternative embodiments are contemplated that may include differentnumbers of phases of a clock cycle assigned to different types offunctions.

During phases B and C a DCP may perform ALU operations, respectivelydenoted “DCP ALU phase 1” and “DCP ALU phase 2” in FIG. 5. During phasesD and A data may be transferred between DCCs. Because the memories maynot be read and written in the same phase, the address decoding logicfor read accesses may be time-shared with the address decoding logic forwrite accesses in address decoders 420. And because the DCPs and DCCsmay not access memory in the same phase, the address decoding logic forDCP accesses may be time-shared with the address decoding logic for DCCaccesses in address decoders 420. This timing relationship may minimizethe size and complexity of address decoders 420 within each DCC 400,which may reduce IC area and power dissipation. Alternative embodimentsare contemplated that may include different timing relationships andcorrespondingly different address decoder implementations.

It is noted that a memory access error may occur if two or more DCPsattempt to write to the same location of a given multi-port SRAM 425(i.e., a given DCC 400 receives the same address value on at least twoof address ports 403 at the same time). For many SRAM implementations, amemory access error may also occur if the same location issimultaneously read to and written from. Similar errors may occur whencrossbar 450 is writing to multi-port SRAM 425. In one embodiment,memory access errors may be prevented by software programming alone,while in other embodiments, additional hardware may be implemented toprevent such errors. In a software programming embodiment, memory accesserrors at a particular multi-port SRAM 425 may be avoided if all theprograms accessing that SRAM are deterministic and start in asynchronized way. As used herein, a deterministic program refers to aprogram that is predictable in the exact number of cycles required toarrive at any instruction. A program may be deterministic if the numberof cycles required to execute it is not influenced by interrupts or datadependencies. In one software programming embodiment, memory accesserrors may be avoided without requiring strict program determinism ifeach program thread (e.g., a program executing on a particular DCP) thatmay have gone out of synchronization is resynchronized before its nextaccess of shared memory.

In some MMAP embodiments, fully deterministic programming in which allprogram threads maintain synchronization through software design may bevery efficient because no synchronizing, arbitrating, or interlocking(handshaking) steps or circuits may be required. However, other MMAPembodiments may benefit from the increased efficiency of executing allof an application's software in a single IC. In such single-ICembodiments, interrupts and data dependencies that may cause programthread desynchronization may be employed by some subset of DCPs tofacilitate certain application software and interfacing requirements.However, software and hardware design may take such desynchronizationpotential into account, providing sufficient instruction bandwidth suchthat potentially desynchronized program threads may perform handshakingsteps with other processes.

Communication Pathways in the Switched Routing Fabric

In some MMAP embodiments, longer distance communications (i.e.,communications beyond DCPs and DCCs which are adjacent) may be supportedby pathways that may be essentially logical channels. Each pathway maytransport data in only one direction; if two-way communication isrequired, then a second pathway may be established in the oppositedirection. In general, a MMAP embodiment may have multiple connectionlinks between pairs of DCCs formed by space multiplexing or timemultiplexing a plurality of physical connections. Pathways may beestablished over such connection links. However, once a pathway isestablished, it may not change the connection links it uses or the DCCsto which it couples during its existence. Therefore, each pathway may beuniquely defined as an ordered sequence of DCCs and connection links,for example as a first or source DCC, a first connection link, a secondDCC, a second connection link, a third DCC, a third connection link, andso forth to a last or destination DCC. In one embodiment, the set of allthe pathways in a MMAP may be uniquely defined by the state of all thecrossbar configuration registers in all DCCs, such as CCR 451 of FIG. 4.

To support the dynamic configuration of a MMAP, pathways may be createdquickly and destroyed quickly. In some embodiments, pathway creation anddestruction may be initiated by either a given DCP or a given DCC. Forexample, a given DCC may be configured to perform a DMA transfer toanother DCC without DCP intervention, and thus may be configured tocreate and destroy a pathway. Two methods that may accomplish dynamicpathway creation and destruction include global programming and wormholerouting. Pathway creation with global programming is described next,followed by a description of the mode and flow control features that maybe common to many MMAP pathways. A description of the wormhole routingmethod follows the mode and flow control description.

Pathway creation or setup using the global programming method mayrequire that every pathway in the MMAP be defined by software control,and may require that each such pathway be configured before the pathwayis used for data transfer. This may be done either manually by aprogrammer or automatically, for example by a routing compiler orauxiliary software or by selecting a library function where the functioncode already includes pathway setup. If an ensemble of pathways is to beused simultaneously in the MMAP, then it may be up to the programmer toensure that they do not use more communication link resources than areavailable in the hardware. Alternatively, software tools may be used toaccount for link resource usage.

To create a single pathway with global programming, several instructionsmay be loaded into the communication controllers, such as communicationcontroller 430 of FIG. 4, within the DCCs along the pathway. Theinstructions may load the appropriate crossbar configuration register451 bit-groups associated with each link in the path. In someembodiments, the instructions may do this immediately or in a sequence,while in other embodiments they may await a trigger signal of some sort.In various embodiments the hardware may or may not prevent pathways frombeing interrupted once established. Therefore, it may be theresponsibility of the programmer or routing software to ensure only onepathway is assigned to any given link at a time. Once the crossbarconfiguration registers 451 in the DCCs all along the pathway are set,the communication pathway may be complete and ready for data. A pathwaymay be destroyed when it is no longer required by altering the relatedbit-group in the crossbar configuration registers of every DCC includedin the pathway. Alternatively, an existing pathway may be left intactindefinitely, and the CCR bit-groups of a pathway may simply beoverwritten by new pathways as needed after the existing pathway is nolonger required.

Some MMAP embodiments may provide at least two modes for datatransmission along the pathway: a fully synchronous mode and a partlytransparent mode. In some embodiments, the mode in use at a particularDCC such as DCC 400 of FIG. 4 may be programmed by transparency bitsincluded in the DCC crossbar configuration registers such as CCR 451 ofFIG. 4. In other embodiments, it is contemplated that the datatransmission mode may be programmed by other means.

FIG. 6—Timing Diagram of a Synchronous Data Transmission Mode

FIG. 6 is a timing diagram illustrating the operation of one embodimentof a synchronous data transmission mode. In FIG. 6, a number ofmulti-phase clock cycles are illustrated along the horizontal axis. Theillustrated clock cycles may be exemplary of clock cycle 500 of FIG. 5.Selected subunits of DCCs within a MMAP are illustrated along thevertical axis, and data progress through the selected subunits isillustrated within the body of the timing diagram.

Referring collectively to FIG. 4 through FIG. 6, in the fullysynchronous data transmission mode, output registers 455 may beconfigured to be clocked once each clock cycle by the output latchsignal conveyed from routing logic 435. Data words may be bufferedwithin each output register 455 in each DCC in the path from a sourcenode to a destination node. If there is no blockage from conditionsfurther down the path, then routing logic 435 may configure inputregisters 454 at each DCC in the path to be transparent. As used herein,transparent register operation refers to a mode of operation in which aninput to a register may pass directly to an output of that registerwithout being gated by or synchronized to a clock or any other signal.When operating in a transparent mode, changes in a signal at the inputof a register may be reflected in the output of that registerimmediately upon propagating through the register circuitry.

Once a fully synchronous transmission path is setup, for example by theglobal programming method discussed above, data may traverse the path asfollows. The source DCP may first write a first word denoted W1 to theSRAM1 source memory location in multi-port SRAM 425 of a neighboring DCC400. In FIG. 6, this write may occur during phase D of the clock cycle1, but for simplicity is not depicted. The first word W1 may be held inlocation SRAM1 through phases A, B, and C. Crossbar 450 of theneighboring DCC is denoted X-bar 1 in FIG. 6. X-bar 1 may read data wordW1 during phase C of the clock cycle 2, and may hold it in one of outputregisters 455 during phases D, A, B and C for transmission to a secondDCC. Crossbar 450 of a second DCC is denoted X-bar 2 in FIG. 6. X-bar 2may latch data word W1 during phase C of clock cycle 3, and may hold itin one of output registers 455 during phases D, A, B, and C fortransmission further downstream.

In FIG. 6, the waveforms shown for each X-bar reflect changes at theoutput of each respective output register. Since the data word intransit may be buffered in a given output register 455 during a givenphase C, the path may receive another data word from a previous DCC orfrom the DCP via the SRAM source memory location without losing thepreviously received data word. Data words may be buffered in outputregisters 455 along the pathway. Crossbar 450 of the destination DCC isdenoted X-bar 4 in FIG. 6. When the data word in transit reaches thedestination DCC, X-bar 4 may write the data word W1 to the SRAM4destination memory location of the destination multi-port SRAM 425during phase B of cycle 6. SRAM4 may hold data word W1 during phases C,D, and A, so that a destination DCP may read data word W1 from SRAM4during phase A of cycle 7. The path may deliver another data word duringthe following clock cycle, and this may be repeated indefinitely. It isnoted that although four intervening crossbars are illustrated in thedata transfer between source location SRAM1 and destination locationSRAM4, a given data transfer may traverse an arbitrary number ofcrossbars in an arbitrary number of DCCs.

FIG. 7—Transparent Mode Data Transfer

Referring to the data transfer example illustrated in FIG. 6, a path maybe set up for quicker delivery of data if input registers 454 and outputregisters 455 of some DCCs in the communication pathway are placed intransparent mode.

FIG. 7 is a timing diagram illustrating the operation of severalembodiments of a transparent data transmission mode. In FIG. 7, a numberof multi-phase clock cycles are illustrated along the horizontal axis.The illustrated clock cycles may be exemplary of clock cycle 500 of FIG.5. Selected subunits of DCCs within a MMAP are illustrated along thevertical axis, and data progress through the selected subunits isillustrated within the body of the timing diagram.

FIG. 7 illustrates the same data transfer example path between sourcelocation SRAM1 and destination location SRAM 4 as depicted in FIG. 6,for two alternative cases of transparent register configuration.Referring collectively to FIG. 4 and FIG. 7, in the first case, outputregisters 455 associated with X-bar 1 may be configured as synchronousor “clocked,” and input registers 454 and output registers 455associated with X-bars 2 through 4 may be configured as transparent. Asdistinct from the fully synchronous example of FIG. 6, FIG. 7illustrates for the first case that once data word W1 is launched fromoutput registers 455 of X-bar 1, it propagates transparently through theoutput registers 455 of X-bars 2 through 4, incurring only the timerequired to propagate through DCC logic and interconnect. FIG. 7illustrates that for the first case, data word W1 may arrive at thetransparent output register 455 of X-bar 4 with very little time to setup for phase B of clock cycle 3 where it may be written to locationSRAM4. A programmer may determine if the timing margin is adequate inthis case to complete the data transfer without error.

In the second case, output registers 455 associated with X-bar 4 may beconfigured as synchronous rather than transparent. For this case, FIG. 7illustrates that data word W1 may be captured by output registers 455 ofX-bar 4 during phase C of cycle 3 and held at the output of theseregisters from phase D of cycle 3 through phase C of cycle 4. Thisconfiguration may provide sufficient margin to write data word W1 tolocation SRAM4 in phase B of cycle 4. Even in the second case, data wordW1 may be written to location SRAM4 in the 4^(th) cycle, compared to the6^(th) cycle in the fully synchronous case illustrated in FIG. 5. Overlonger paths the time savings afforded by transparent data transmissionmode data transfer may be even greater.

FIG. 8—Configurable Mode Data Transmission

FIG. 8 is a flow diagram illustrating the operation of one embodiment ofconfigurable mode data transmission in a MMAP. Referring collectively toFIGS. 1, 4, 7, and 8, operation begins in block 800 where a pathway froma source node to a destination node is configured. In one embodiment,the source node may be a DCP, while in another embodiment, the sourcenode may be a DCC configured to perform a DMA transfer, for example. Inone embodiment, the pathway may be configured using the globalprogramming method described above, while in other embodiments, thepathway may be configured using wormhole routing or anotherconfiguration method.

After the pathway has been configured, the output registers 455 of eachDCP 400 along the pathway from the source node to the destination nodemay be configured to operate in either a synchronous data transfer modeor a transparent data transfer mode (block 802). In an alternativeembodiment, this step may be performed concurrently with the pathwayconfiguration performed in block 800.

Once transfer mode configuration is complete, the source node maytransmit a data word to the destination node (block 804). Each data wordtransmitted may continue through the flow diagram from block 806, whilethe source node operation may continue from block 816. Referring toblock 806, output registers 455 of a given intermediate DCC node in thepathway from the source node to the destination node may be configuredto operate in synchronous mode or transparent mode. If synchronous modeis the case, the data word may be captured in one of output registers455 and held until the next clock cycle (block 808) before proceeding tothe next DCC in the pathway (block 810). If transparent mode is thecase, the data word may propagate directly to the next DCC in thepathway without being gated by a clock signal (block 810). If the nextDCC in the pathway represents the destination DCC (block 812), thedestination DCC may write the data into multi-port SRAM 425 during thenext available write phase (block 814). At this point, transfer of thedata word may be complete. Otherwise, operation may continue from block806, wherein the data transfer mode of the current DCC is determined.

Referring to block 816, once the source node has transmitted a data wordit may determine whether the current data transfer is complete. If not,the source node may transmit another data word to the destination node(block 804). Otherwise, the source node may determine whether it hasanother data transfer to initiate to the current destination (block818). If so, the source node may reconfigure the data transfer modeconfiguration of each DCC 400 along the pathway (block 802). In analternative embodiment, the source node may configure the data transfermode configuration and the pathway concurrently and may retain the datatransfer mode configuration throughout all data transfers to the samedestination, eliminating block 808.

Returning to block 818, if the source node has no more data to transferto the current destination, it may determine whether it has anothertransfer to initiate to a different destination (block 820). If so, apathway may be configured to the new destination (block 800). Otherwise,the source node may enter an idle state (block 822).

It is noted that in some DCC or MMAP embodiments, multiple datatransfers may be configured to occur to multiple destination nodessimultaneously.

Address Sequencing and DMA

In the above descriptions of data transfer, the source or destinationSRAM memory location addresses may be fixed or may change every clockcycle in a specified sequence. If the address is fixed then the DCC oran adjacent DCP may directly service the specified memory location forarriving or departing words. If the address is stepped in a sequencethen multi-port SRAM 425 may function as a buffer for the word traffic,but the addresses may be provided to it from either the DCCcommunications controller 430 or from an adjacent DCP. Appropriateaddress generation may be achieved, for example, by the DMA capabilityof communication controller 430. A DMA operation may require a startaddress, stop address, and stride for access to a buffer array inmulti-port SRAM 425. Processes in the adjacent DCPs may access thebuffer array. Since the buffer is finite, it may be subject to overflow,in case the buffer fills before a DCP is able to consume data, andunderflow, in case a DCP attempts to consume data before it has arrived.Therefore, the interaction of DMA with processes running on the adjacentDCPs may need to be coordinated by software control. In addition, theDCCs may provide some hardware assistance for managing data word flowcontrol on the pathways, described next.

Flow Control

Normally all the words in a pathway may make progress towards theirdestination on every clock cycle. However, the production andconsumption of data by the source and destination DCCs may be uneven.For these situations the DCCs may include flow control means to startand stop the sequence of words in the pathway.

Additional circuits may be needed to support flow control. Multi-portSRAM 425 may include an additional bit for some or all memory locationaddresses. This extra bit, which may be referred to as a “handshakebit”, may be read and written by DCPs to coordinate word transferthrough the memory locations that are configured to include it. If thehandshake bit is asserted, it may indicate that the producer process ina source DCP may wait until the consumer process in a destination DCPreads the data and clears the bit. If the handshake bit is de-asserted,then the producer process may write a word to the location. The samemechanism can be used to coordinate the transfer of words to or frommemory by DCCs. It is noted that in some embodiments, assertion of asignal may refer to driving that signal to a logic 1, and de-assertionof a signal may refer to driving that signal to a logic 0, while inother embodiments, the polarities of any given signal may be reversedwith respect to assertion and de-assertion.

More circuits may be needed to support flow control over longer distancepaths involving multiple DCCs. Each connection link from DCC to DCC mayinclude an “idle” (also denoted IDL) line sent forward along the linktowards a receiving DCC and a “blocked” (also denoted BLK) line sentbackward along the link towards a sending DCC. Looking at a wholepathway, the signal for the idle line may ultimately derive from ahandshake bit in the SRAM source location, and the signal for theblocked line may derive from a handshake bit in the SRAM destinationlocation.

When a message (an ordered sequence of words) becomes blocked in oneMMAP embodiment, for example due to a stall at the destination node orat an intermediate node, the blocked message may be stored in inputregisters 454 and output registers 455 of DCCs in the pathway. Theprocess by which the message is halted may include a back propagation ofthe assertion of the BLK signal toward the data source node. The BLKsignal may traverse one DCC per clock cycle, unless the output registers455 of a given DCC are configured to operate in transparent mode, inwhich case multiple DCCs may be traversed in a given clock cycle. Ateach DCC output register 455 which is configured to operate insynchronous mode, the arrival of a BLK signal may inhibit the update ofoutput register 455 and may cause it to “freeze” or capture and retain aword of the message therein. Since the next word of the message mayarrive at input register 454 in the same cycle that the output register455 is frozen, the arrival of the BLK signal may also enable the captureand retention of the input word in input register 454 during the samecycle. As the BLK signal propagates to the data source, it may freezethe data words in the pathway at two words per DCC, one in inputregister 454 and one in output register 455. If the cause of the firstBLK signal is removed, the de-assertion of the BLK signal may bepropagated towards the data source in a manner similar to the BLKassertion propagation. In this case, a “melting front” corresponding tothe initial data freezing may propagate toward the data source, exceptthat the BLK de-assertion may release words to move towards thedestination at the rate of one word per cycle, beginning with the frozenregister closest to the destination node.

As described above, a stall at a destination or intermediate node maycause the source node to stall, and may thereby prevent a source nodefrom overflowing a destination node with data (i.e., prevent a sourcenode from generating data faster than a destination can consume it). Asimilar condition may occur if a source node stalls during generation ofa data transfer. For example, a source node may set up a pathway to adestination node, send a quantity of data, and then become idle whilewaiting for additional data to arrive from a third node. Similarly, ablockage may occur at an intermediate node, preventing additional datafrom the source node to the destination node. In such a case, if thedestination node is not advised that data arrival has stopped, it mayincorrectly continue processing. For example, a destination node may beprogrammed to continuously loop through the contents of a bufferconfigured within a given DCC, and may assume that the buffer will becontinuously refreshed with new data. However, if the source node stallsand the destination node continues processing the buffer contents, thedestination node may incorrectly process stale data as though it werenew data. Such a condition may be referred to as underflow.

In one embodiment, when data flow from a source node to a destinationnode stops, for example due to a stall at the source node or anintermediate node, the stalling node may assert an IDL signal associatedwith the connection link implementing the pathway from the source nodeto the destination node. The assertion of the IDL signal may bepropagated forward towards the destination node. When the destinationnode receives the assertion of the IDL signal, it may take a predefinedaction in response. For example, in one embodiment, a destination nodemay enter an idle state in response to receiving an assertion of the IDLsignal associated with a particular connection link. In someembodiments, the response of a destination node to an assertion of anIDL signal may be determined by hardware design, while in otherembodiments, the response may be software programmable.

In one embodiment, the IDL signal may be used to keep an establishedpathway open even though no data transfer is taking place. In such anembodiment, a source node may create a pathway to a destination node andmay use it to transfer multiple data words over a period of time, withidle periods of arbitrary length (also referred to as “gaps”) occurringbetween any given transferred data words. Such an embodiment may enablemore efficient data transfer, as it may enable a reduction in the numberof pathway creation and destruction operations associated withtransferring a given amount of data.

FIG. 9 is a flow diagram illustrating the operation of one embodiment offlow control in a MMAP. The operation shown in FIG. 9 may beillustrative of either the propagation of “blocked” stalling informationfrom a destination node toward a source node or the propagation of“idle” stalling information from a source node toward a destinationnode, as described above. The operation shown in FIG. 9 is firstdescribed with respect to propagation of stalling information from adestination node toward a source node. Referring collectively to FIGS.1, 4, and 9, operation begins in block 900 where a pathway from a sourcenode to a destination node is configured. In one embodiment, the sourcenode may be a DCP, while in another embodiment, the source node may be aDCC configured to perform a DMA transfer, for example. In oneembodiment, the pathway may be configured using the global programmingmethod described above, while in other embodiments, the pathway may beconfigured using wormhole routing or another configuration method.

After a pathway is configured, the source node may begin transferringdata to the destination via the pathway (block 902). During thetransfer, the destination node or one or more of the intermediate nodesbetween the source and destination nodes may stall, and the stallcondition may be detected (block 904). For example, the destination nodemay be unable to consume the data transfer due to other processingtasks, or the transfer may be interrupted at an intermediate node. If astall has not been detected, the destination node may determine whetherit has received the complete data transfer, for example, by detectingwhether it has received the tail of a worm (as described below in thesection on wormhole routing) or by detecting a control messageinstructing the teardown of the pathway (block 906). If the datatransfer is complete, the destination node may enter an idle state toawait another data transfer or another task (block 908). If the datatransfer has not yet completed, data may continue progressing from thesource node to the destination node via intermediate nodes along thepathway (block 910). While data is in transit, stalls may continue to bemonitored and detected (block 904).

If a stall has been detected, stalling information may be propagatedfrom the stalling device upstream through the pathway towards the sourcenode. In one embodiment, such stalling information may be propagated viaassertion of a BLK signal associated with the pathway. As the stallinginformation propagates, data words in transit may be captured withineach node along the pathway. In one embodiment, a data word may becaptured within input registers 454 of a stalling DCC or the DCC coupledto a stalling DCP, and the stalling information propagated to the firstupstream DCC. A pathway may traverse a DCC through one output register455, and one input register 454. One data word may be captured withineach of the assigned output register 455 and the assigned input register454 of the first upstream DCC, and the stalling information propagatedto the next upstream DCC. Specifically, in one embodiment routing logic435 of a given DCC may be configured to receive propagated stallinginformation and to configure output registers 455 and input registers454 to capture data through the use of respective output latch and inputlatch signals. In one embodiment, the data capture and stall propagationmay continue in the above fashion until the source node is reached. Insuch an embodiment, the source node may be configured to suspend datatransfer in response to receiving the propagated stalling information(block 912).

Once a stall has been detected, the stalling node may determine that ithas become available to communicate and resume the stalled data transfer(block 914). If the stalled node has not become available tocommunicate, it may wait to become available (block 916) and continuetesting to determine whether it has done so (block 914). If the stallednode has become available to communicate, availability information maybe propagated from the stalling device upstream through the pathwaytowards the source node. In one embodiment, such availabilityinformation may be propagated via de-assertion of a BLK signalassociated with the pathway. As the availability information propagates,data words captured in transit by the propagation of stallinginformation may be released to continue along the pathway towards thedestination. In one embodiment, a data word captured within inputregisters 454 of a stalling DCC or the DCC coupled to a stalling DCP,may be released and the availability information propagated to the firstupstream DCC. A data word captured within output registers 455 of thefirst upstream DCC may be released, followed by a data word capturedwithin input registers 454 of the first upstream DCC, and theavailability information propagated to the next upstream DCC.Specifically, in one embodiment, routing logic 435 of a given DCC may beconfigured to receive propagated availability information and toconfigure output registers 455 and input registers 454 to release datathrough the use of respective output latch and input latch signals. Insuch an embodiment, the data release and availability propagation maycontinue in the above fashion until the source node is reached, and thesource node may be configured to resume data transfer in response toreceiving the propagated availability information (block 918). Once theavailability information has completely propagated through the pathway,data may continue progressing from the source node to the destinationnode via intermediate nodes along the pathway (block 910).

The operation shown in FIG. 9 is now described with respect topropagation of stalling information from a source node to a destinationnode. Again referring collectively to FIGS. 1, 4, and 9, the pathwayconfiguration performed in block 900 may occur as described above. Aftera pathway is configured, the source node may begin transferring data tothe destination via the pathway (block 902). During the transfer, thesource node or one or more of the intermediate nodes between the sourceand destination nodes may stall, and the stall condition may be detected(block 904). For example, the source node may be unable to continuetransferring data due to other processing tasks, or the transfer may beinterrupted at an intermediate node.

If a stall has not been detected, the source node may determine whetherit has transmitted the complete data transfer, for example, by detectingwhether it transmitted the tail of a worm (as described below in thesection on wormhole routing) or by transmitting a control messageinstructing the teardown of the pathway (block 906). If the datatransfer is complete, the source node may enter an idle state to awaitanother data transfer or another task (block 908). If the data transferhas not yet completed, data may continue progressing from the sourcenode to the destination node via intermediate nodes along the pathway(block 910). While data is in transit, stalls may continue to bemonitored and detected (block 904).

If a stall has been detected, stalling information may be propagatedfrom the stalling device downstream through the pathway towards thedestination node. In one embodiment, such stalling information may bepropagated via assertion of an IDL signal associated with the pathway.As the stalling information propagates towards the destination node,data words in transit downstream from the stalling device may continueto propagate towards the destination node. In one embodiment, the stallpropagation may continue in the above fashion until the destination nodeis reached. In such an embodiment, the destination node may beconfigured to suspend data processing in response to receiving thepropagated stalling information (block 912).

Once a stall has been detected, the stalling node may determine that ithas become available to communicate and resume the stalled data transfer(block 914). If the stalled node has not become available tocommunicate, it may wait to become available (block 916) and continuetesting to determine whether it has done so (block 914). If the stallednode has become available to communicate, availability information maybe propagated from the stalling device downstream through the pathwaytowards the destination node. In one embodiment, such availabilityinformation may be propagated via de-assertion of an IDL signalassociated with the pathway. In such an embodiment, the availabilitypropagation may continue in the above fashion until the destination nodeis reached, and the destination node may be configured to resume dataprocessing in response to receiving the propagated availabilityinformation (block 918). Once the availability information hascompletely propagated through the pathway, data may continue progressingfrom the source node to the destination node via intermediate nodesalong the pathway (block 910).

For simplicity, FIG. 9 illustrates detection and propagation of a singlestall followed by propagation of availability information correspondingto that stall. However, in one embodiment, it is contemplated thatmultiple stalls of the same type (e.g., BLK or IDL) may occur during thecourse of a data transfer. For example, in such an embodiment, it iscontemplated that new stalling information may propagate upstream from astalling device towards a source node before availability informationresulting from the resolution of a previous stall has completelypropagated upstream towards the source node. If the order of propagationof stalling information and availability information is preserved (i.e.,a second stalling information does not propagate upstream ahead of afirst stalling information or a first availability information), eachoccurrence of stalling and availability may be understood in terms ofthe relevant portion of FIG. 9. It is further contemplated that multiplestalls of different types (e.g. BLK and IDL) may occur during the courseof a data transfer. For example, both a source node and a destinationnode may stall and propagate respective stalling information toward eachother. In such an embodiment, each stalling node may be required topropagate respective availability information before data transferprogress may resume.

It is noted that in one embodiment, the flow control operation of FIG. 9may be combined with the configurable mode data transmission of FIG. 8.In such an embodiment, data progressing from a source node to adestination node may propagate across more than one intermediate node ina given clock cycle if such intermediate nodes have been configured tooperate in a transparent data transfer mode, as described above.Likewise, in such an embodiment, stalling and availability informationmay propagate across more than one intermediate node in a given clockcycle if such intermediate nodes have been configured to operate in atransparent data transfer mode. In one embodiment including the flowcontrol operation of FIG. 9 and the configurable mode data transmissionof FIG. 8, for a given intermediate DCC node receiving propagatedstalling information as described above, data may be captured withininput registers 454 and output registers 455 only if those outputregisters have been configured to operate in a synchronous data transfermode.

Wormhole Routing

To support pathway setup by wormhole routing, some MMAP embodiments mayprovide some additional circuits. These may include, for each DCC-typeport, an additional control line indicating control/data status anddenoted C/D, which may be included in every connection link between DCCsand coupled to routing logic 435 in each DCC. The maximum number ofwires in the connection link may nominally correspond to the sum of thenumber of bits per data word, plus one wire each for C/D, IDL, and BLK.However, in some MMAP embodiments these signals may be multiplexed in anumber of different ways to reduce total wire count.

As data words are received at one DCC from another DCC, the C/D bit mayused by the receiving DCC to distinguish header, body, and tail words ofa worm. If the C/D bit is de-asserted, it may indicate that the receivedword is a body word. A body word may correspond to a data word plus thecontrol bit, which may be passed along the pathway unchanged. If the C/Dbit is asserted, it may indicate that the received word is a controlword. A control word may allow the data portion of the word to contain arouting code for interpretation by routing logic 435.

One important feature of the routing code may be an indication ofwhether the control word is a header or a tail; thus, an H/T bitindicating header/tail status of a control word may be provided. In oneembodiment, the H/T bit may be adjacent to the C/D bit, but in otherembodiments it may be assigned to other bit positions or maybe aspecific multibit code. If the control word is a tail word, then it maybe propagated along the pathway and may sequentially free DCC outputports for use by some other pathway.

If a control word is a header word it may be latched within inputregister 454 of the receiving DCC and decoded by combinatorial logic inrouting logic 435. Routing logic 435 may examine the rightmost severalbits of the header word as well as the port from which the header came,and may issue a request of crossbar 450 for an output port as shown inTable 1. The several bits examined by routing logic 435 for the purposeof requesting an output port may be referred to as a navigation unit, orNUNIT. For a DCC embodiment that includes four DCC-type output ports perDCC, a NUNIT may use a two-bit code to specify the four directionoptions, as shown in Table 1. In other embodiments that include the sameor different numbers of DCC-type ports, other NUNIT codes may be used. Acode using two bits per NUNIT is described below. If the output port isnot blocked by an already established pathway then routing logic 435 mayevaluate the NUNIT and allow the worm to proceed. For example, if aheader word arrived from SRAM with a NUNIT code of 10, routing logic 435may request the East output port from crossbar 450 for the header wordand subsequent words of this worm.

TABLE 1 Output port as a function of direction code and input port.Input ports Direction (code) North East South West SRAM Straight through(11) S W N E N Left turn (10) E S W N E Right turn (01) W N E S S Null(00) SRAM SRAM SRAM SRAM W

FIG. 10 illustrates operation of one embodiment of routing logic on aheader word. FIG. 10 depicts a header word as it progresses throughmultiple DCC nodes on a pathway from a source node to a destinationnode. Case (a) may illustrate a header word in its initial stateoriginating in a source DCC. In this state, the header word includes aC/D bit, an H/T bit, and a plurality of header NUNIT fields numbered HN0through HN4, with HN0 occupying the least significant bits of the headerword.

At each DCC including the source and destination DCCs, the header wordmay be passed on to the output of the crossbar with modification asfollows. The header word may be right shifted by one NUNIT and filledwith zeroes from the left. The C/D and H/T bits may then be restored totheir original positions. Cases (b) through (e) of FIG. 10 mayillustrate the header modification that occurs after the header has beenprocessed by one through four DCCs, respectively. As it passes througheach DCC the lead header word may fill with more zeroes until the nullcode is in the rightmost NUNIT, as shown in case (e). If the null codeis the rightmost NUNIT when the header word is not from the same DCC(controller or neighbor DCP), and the next worm word is not a controlword, then the header word may be at the destination DCC for that worm.

The check for arrival at the destination DCC may require multipleclocks. First the lead header word may be moved into one of inputregisters 454 and tested by the routing logic 435 for the null code inthe rightmost NUNIT. If the null code is found, then in the next clockcycle the next word of the worm may overwrite the lead header word andits C/D and H/T bits may be tested. If the next word is another headerword then it may become the new lead header word, and its rightmostNUNIT may be used to select the output port for the next DCC. There maybe many header words per worm in order to route across large arrays. Ifthe next word is a body word rather than a header word, the worm may beat its destination DCC. In this case the body word may be written to apreset SRAM location in the DCC. The arrival of a body word at alocation may be detected by the DMA logic of communication controller430, or by a DCP, either of which may service the arrival of subsequentbody words. Information regarding how to service the worm may either bepreloaded at the destination node or included in the worm right afterthe header.

FIG. 11 is a block diagram illustrating an example pathway through aportion of a MMAP. FIG. 11 depicts eight crossbars denoted “Crossbar A”through “Crossbar H”. Each depicted crossbar may be exemplary ofcrossbar 450 of FIG. 4. Although the additional logic is not shown forsimplicity, each depicted crossbar may be included in a respective DCCsuch as DCC 400 of FIG. 4, and each such DCC may be coupled to otherDCCs within a MMAP embodiment such as the embodiment illustrated in FIG.2.

In the illustrated embodiment of FIG. 11, each of crossbars A-H includesfour input ports denoted N, S, E, and W on the left edge of the crossbaras well as four output ports denoted N, S, E, and W on the right edge ofthe crossbar. Each crossbar's input ports may be coupled to DCC inputports 404 of the respective DCC, and each crossbar's output ports may becoupled to DCC output ports 405 of the respective DCC. Additionally,each of crossbars A-H includes an input connection and an outputconnection to a memory, such as multi-port SRAM 425 of FIG. 4, whichconnection is denoted M on the left and right edges of the crossbar,respectively.

In the illustrated embodiment, each crossbar A-H is coupled to aplurality of neighboring crossbars via each respective DCC such thateach output port N, S, E, W of each crossbar is coupled to a respectiveinput port S, N, W, E of each of the plurality of neighboring crossbars.Thus, in the illustrated embodiment, each crossbar may be coupled toreceive inputs from and send outputs to four neighboring crossbars. Itis noted that in alternative embodiments, it is contemplated that adifferent number of crossbars may be provided, each comprising adifferent number of input ports, output ports, and memory connections.

FIG. 11 illustrates a pathway from a source DCC including crossbar A toa destination DCC including crossbar H, which pathway traverses DCCsincluding crossbars B, F, and G. Referring collectively to FIG. 10 andFIG. 11, a 2-bit NUNIT code defined according to Table 1 may be used toimplement the illustrated pathway as follows. The pathway originates inthe SRAM coupled to crossbar A via input memory connection M and exitscrossbar A via output port E. According to Table 1, the NUNIT forcrossbar A should be 10. Output E of crossbar A is coupled to input W ofcrossbar B, and the illustrated pathway exits crossbar B via output portS. According to Table 1, the NUNIT for crossbar B should be 01. Output Sof crossbar B is coupled to input N of crossbar F, and the illustratedpathway exits crossbar F via output port E. According to Table 1, theNUNIT for crossbar F should be 10. Output E of crossbar F is coupled toinput W of crossbar G, and the illustrated pathway exits crossbar G viaoutput port E. According to Table 1, the NUNIT for crossbar G should be11. Finally, output E of crossbar G is coupled to input W of crossbar H,and the illustrated pathway ends in the SRAM coupled to crossbar H viaoutput memory connection M. According to Table 1, the NUNIT for crossbarH should be 00.

Thus, a header control-word implementing a wormhole routing in theformat of FIG. 10 for the path illustrated in FIG. 11 may include anasserted C/D bit indicating a control word, an asserted H/T bitindicating a header word, and the values 00,11, 10, 01, and 10corresponding to fields HN4 through HN0, respectively. It is noted thatthe illustrated pathway is merely one of many possible pathways throughone MMAP embodiment. It is contemplated that other pathways may beconfigured using wormhole routing or other routing methods, and thatother embodiments may include different numbers of crossbars and portsinterconnected in different fashions.

Since each NUNIT may be consumed by a specific DCC along a pathway, oneor more bits may be added to each NUNIT to request specific behavior atindividual DCCs. For example, in one embodiment, one added bit per NUNITmay be used to specify that a given DCC shall operate in a transparentor synchronous data transfer mode, as described above. In such anembodiment, a wormhole-routed path may be fully synchronous or partlytransparent depending on the programming of transparency bits in theheader word.

In another embodiment, a DCP may send a header word directly to thecrossbar inputs of a neighboring DCC such as DCC 400 of FIG. 4. A DCPmay do so by specifying a particular address to a neighboring DCC viaDCP address ports 403 of that DCC, and sending the header word via DCPinput ports 401 of that DCC. Routing logic 435 may be configured to thensend the worm on its way to its destination without using the multi-portSRAM 425. This technique may provide a message passing capabilitybetween DCPs.

Collision Handling

A pathway being set up by wormhole routing may collide with an existingpathway or one or more other pathways being wormhole routed through agiven DCC at the same time. A collision may occur when one or moreheader words requests the same crossbar output port at the same time, orwhen the output port is already occupied by a pathway. Routing logic 435may include logic configured to arbitrate which pathway receives accessto the contested output port in case of a collision. Routing logic 435may detect the collision and grant only one worm access to the contestedoutput port. Various priority/rotation schemes (e.g., a round-robinscheme) may be used to shape the traffic distribution and ensure that noinput port is always refused access to a requested output port.

When a pathway being initially set up by wormhole routing is blocked, itmay be advantageous to stop the forward progress of the blocked wormwithout destroying it. In this case, the flow control mechanismdescribed above may be employed. For example, the header of the worm maybe latched in input registers 454 of the blocking DCC, and the BLKsignal may be driven to the next upstream DCC in the path to latchanother segment of the worm in input registers 454 of the next upstreamDCC. This process may be repeated back to the DCC containing the tailword of the worm, or to the source DCC if the tail word has not yet beentransmitted. The data in the worm may be captured in the input registers454 and output registers 455 of DCCs in the pathway that are configuredto operate in a synchronous data transfer mode. As described above, twowords may be stored per DCC, resulting in a “scrunched” or “telescoped”condition of the stalled worm. The worm may stay frozen indefinitelyuntil the blocking conditions go away, following which its forwardmotion may be automatically restarted by the propagation of thede-assertion of the BLK signal.

Several example applications illustrating MMAP functionality arediscussed below. It should be noted that such examples are not intendedto limit the structure, function, or scope of a MMAP or its components,but are intended only to facilitate understanding of the foregoingdescription. It is contemplated that numerous variations of theseexamples may be employed, and that there may be numerous alternativeapplications to the ones discussed below.

EXAMPLE 1 Fast Fourier Transform

In this example a complex waveform in the time-domain may be transformedto the frequency domain using a complex Fast Fourier Transform (FFT).This example may illustrate cooperative processing in which the DCPs aretightly coupled by a deterministic program in fully synchronous mode.

The waveform may be represented by a sequence of time-domain sampleswith uniform periodicity at some multiple of the clock cycle. Topreserve phase information in the waveform, each sample may be treatedas a complex number. Complex numbers may be represented in the computeras a pair of regular fixed or floating-point numbers, one for the realcomponent and the other for the imaginary component of the complexnumber. In this example each regular number may be stored in one word.

The length of an FFT may be defined as the number of samples in thesampled time domain which are processed together to give an output valuein the Fourier domain. The FFT length may also define the number ofdiscrete frequencies in the output spectrum. In a computer the samplesmay be stored in a data array. In this example, eight samples arearranged in a data array, then a length-8 FFT algorithm is performedresulting in eight output values, one output value for each frequency.Finally the eight output values may be sequenced out of the MMAP.

A Fast Fourier Transform (FFT) may comprise several to many stages,where each stage performs complex multiplications, additions, andsubtractions on an array of data. For a Radix-2 FFT, there are N stageswhere 2^(N) is the number of input values. For example, in a length-8FFT, there are eight input values. Since 8=2³, N=3, and therefore thereare three stages for the length-8 FFT. For one FFT algorithmimplementation, each one of these stages may require a total of 32computations. These computations consist of 4 complex multiplications, 4complex additions, and 4 complex subtractions. Each complex addition andsubtraction requires two addition or subtraction computations, as thereal and imaginary portions of each complex number are evaluatedseparately. Likewise, each complex multiplication requires fourmultiplication/multiply-accumulate operations, as both the real andimaginary portions of the multiplier are multiplied against the real andimaginary portions of the multiplicand. Thus, one FFT stage may require8 additions, 8 subtractions, and 16 multiply/multiply-accumulateoperations.

For all three stages of the length-8 FFT, there may be 96 totalcomputations that have to take place. However, since the complexmultiplier used in the first stage has a real value of 1 and animaginary value of 0, the complex multiplications in the first stage donot have to be performed, since for this multiplier value the complexproduct equals the multiplicand. Taking this property into account,there may be a total of 80 computations that have to take place.

For a length-8 FFT, there are 8 complex data points. At each FFT stage,calculations may be performed on pairs of complex data, whichcalculation may be referred to as a butterfly computation. For example,at each stage, a complex multiplication may be performed on one of thepair of complex data points and a complex coefficient. The result is acomplex product that may used for the complex additions and subtractionsat that stage.

Referring now to FIG. 12, a flow diagram illustrating data flow in oneembodiment of a butterfly calculation is shown. The butterflycalculation of FIG. 12 receives two complex input values A and B, aswell as a complex coefficient W, and produces two complex output valuesA′ and B′. The butterfly calculation performs a complex multiplicationbetween complex input value B and complex coefficient W to produce anintermediate complex product Y. The butterfly calculation then performsa complex sum and complex difference calculation between complex inputvalue A and complex product Y to produce complex output values A′ andB′, respectively.

The complex arithmetic operations described above may be represented asoperations on real and imaginary parts of each operand as follows:

Y_real=(B_real*W_real)−(B_imag*W_imag)

Y_imag=(B_real*W_imag)+(B_imag*W_real)

A′_real=A_real+Y_real

A′_imag=A_imag+Y_imag

B′_real=A_real−Y_real

B′_imag=A_imag−Y_imag

In one MMAP embodiment, two adjacent DCPs may be configured to performthe complex computations at the same time while sharing the same data.The first DCP may perform the complex multiplication to generate thereal part of the product, Y_real, and the second DCP may perform thecomplex multiplication to generate the imaginary part, Y_imag. Then, thefirst DCP may perform the complex addition to generate A′_real andA′_imag, and the second DCP may perform the complex subtraction togenerate B′_real and B′_imag. By placing the results in the sharedmemory between the DCPs, each result value may be made available to theother DCP(s) at the next clock cycle following result generation.

FIG. 13 is a block diagram of a portion of a MMAP embodimentillustrating data sharing. FIG. 13 depicts a portion of a MMAPembodiment including DCP1 and DCP2, each of which may be exemplary ofDCP 300 of FIG. 3. Each of DCP1 and DCP2 is coupled to DCC1 and DCC2, aswell as a plurality of other DCCs, each of which may be exemplary of DCC400 of FIG. 4. For simplicity, only a portion of the connections areshown in FIG. 13.

DCP1 may be configured to perform the real portion of the complexmultiplication of the butterfly calculation described above and to storeits result in DCC1, as indicated by the connection from DCP1 to DCC1.Similarly, DCP2 may be configured to perform the imaginary portion ofthe complex multiplication described above and to store its result inDCC2, as indicated by the connection from DCP2 to DCC2. DCP1 and DCP2may be configured to perform their respective portions of the complexmultiplication simultaneously, such that each portion of the complexresult is available to be read by both DCP1 and DCP2 during thefollowing cycle. This availability is indicated by the connections fromeach of DCCT and DCC2 to each of DCP1 and DCP2.

DCP1 may then be configured to perform the complex addition of thebutterfly calculation described above, and DCP2 may then be configuredto perform the complex subtraction of the butterfly calculationdescribed above. DCP1 and DCP2 may be configured to perform theirrespective addition or subtraction simultaneously.

FIG. 13 may illustrate cooperative processing in which the DCPs aretightly coupled by a deterministic program in fully synchronous mode. Inthe illustrated embodiment, each of the DCPs may perform the same numberof arithmetic operations. Since both DCPs may be driven by the samemaster clock, they may operate in lock step for the duration of the FFTcomputation. Data values can be thus shared between each DCP withminimal communication or synchronization overhead.

In one MMAP embodiment, the length-8 FFT computation may be implementedin an array of 8 DCPs. In such an embodiment, the complex computationsof the length-8 FFT may be performed in 11 cycles. The theoreticalminimum latency for the length-8 FFT computation on 8 DCPs, with 80arithmetic operations to be performed, is 10 cycles. In this embodiment,the 11^(th) cycle may be incurred by performing a remote data transferduring the third FFT stage. However, no additional latency due tocommunication overhead may be incurred during the first two stages.

EXAMPLE 2 Vector Arithmetic

The MMAP includes a common memory structure in the DCC that may fulfillthe role of both a register file and a primary cache (i.e., L1 cache)for a given DCP. Each DCP coupled to a DCC may have immediate and directaccess to this memory. Example 1 illustrated how the cooperativeprocessing of two adjacent DCPs may efficiently use this memory resourceby directly sharing register contents between processors. It should alsobe noted that further advantage may be obtained through each DCC'sability to flexibly address and communicate data. These capabilities maypermit the extremely efficient processing of vectors and streams ofdata. Consider as a very simple example the task of adding two vectors.If each vector has n elements, then the vector sum will also have nelements, where each element in the sum is the result of adding oneelement from each of the two original vectors. A minimum of n arithmeticoperations may be required to perform this task. On the MMAP, this taskmay be completed with virtually no additional communication overhead,regardless of the magnitude of n and independent of the number of DCPsused for the task.

In one embodiment, a single DCP may be configured to perform the vectoraddition task. If n is relatively large, then the most practicalapproach may be to encode the operations using a simple loop. The MMAPmay implement this loop with a single instruction that would be repeatedn times. At each iteration of the loop, a different source element maybe used from each of the input vectors and a different result elementmay be produced for the output vector. One embodiment of the MMAParchitecture may complete the loop in n cycles. Traditional processorsmay require additional instructions (and possibly additional cycles aswell) for load and store instructions that move the data between thecache and the register file.

In another embodiment, more than one DCP may be used to perform thevector addition task. In such an embodiment, the computation may be spedup in direct proportion to the number of DCPs used. If p DCPs are used,then each DCP may be configured to execute a loop with N iterations,where N is the smallest integer greater than or equal to n/p. As long asthe data required by each DCP is available in an adjacent DCC, asingle-instruction loop may be sufficient to perform the computation. Ifthe data is not available in an adjacent DCC, then the communicationsfeatures of the DCC may be used to “stream” the data from where it isstored into an adjacent DCC. In some MMAP embodiments, the datacommunication may occur at the same rate as the computation (e.g., oneword per cycle of the master clock). Due to the highly efficient natureof the MMAP communications architecture, it may be possible to set upthe communications and the instruction inside the loop such that noadditional instructions are required to synchronize with or to load thestreaming data. The processor may automatically synchronize with theincoming data stream using the integrated flow-control mechanismsdescribed above. The data may thereby arrive at the same rate as thecomputation is performed, and the total vector of n elements may beprocessed in N cycles.

Although the system and method of the present invention has beendescribed in connection with the preferred embodiment, it is notintended to be limited to the specific form set forth herein, but on thecontrary, it is intended to cover such alternatives, modifications, andequivalents, as can be reasonably included within the spirit and scopeof the invention as defined by the appended claims.

1. A system, comprising: a plurality of processors; and a plurality ofdynamically configurable communication elements, wherein each of atleast a portion of the dynamically configurable communication elementscomprises a memory and a routing engine; wherein at least some of theprocessors and at least some of the dynamically configurablecommunication elements are coupled together in an interspersedarrangement; wherein a source device is configurable to transfer a dataitem through an intermediate subset of the dynamically configurablecommunication elements to a destination device; wherein the sourcedevice corresponds to a particular one of the processors, a particularone of the dynamically configurable communication elements, or aninput/output device; wherein the destination device corresponds to adifferent one of the processors, a different one of the dynamicallyconfigurable communication elements, or a different input/output device;wherein, in response to detecting a stall after the source device beginstransfer of the data item to the destination device and prior to receiptof all of the data item at the destination device, a stalling device isoperable to propagate stalling information through one or more of theintermediate subset towards the source device; wherein in response toreceiving the stalling information, at least one of the intermediatesubset is operable to buffer all or part of the data item.
 2. The systemof claim 1, wherein the stalling device includes the destination deviceor a member of the intermediate subset.
 3. The system of claim 1,wherein the source device is further configurable to transfer the dataitem to the destination device as one of several data elements of a datapacket, and wherein in response to receiving the stalling information,the source device is operable to suspend transfer of the data packet. 4.The system of claim 1, wherein the at least some of the processors andthe at least some of the dynamically configurable communication elementsare physically stacked on a single integrated circuit substrate suchthat the interspersed arrangement supports a three dimensional matrix.5. The system of claim 1, wherein the at least some of the processorsand the at least some of the dynamically configurable communicationelements are distributed across two or more integrated circuitsubstrates.
 6. The system of claim 5, wherein the two or more integratedcircuit substrates are bonded together.
 7. The system of claim 1,wherein two or more of the processors and two or more of the dynamicallyconfigurable communication elements are coupled together to implement ahypercube topology, wherein the two or more of the dynamicallyconfigurable communication elements form vertices of the hypercubetopology.
 8. The system of claim 1, wherein two or more of theprocessors and two or more of the dynamically configurable communicationelements are coupled together to implement a hypercube topology, whereinthe two or more of the processors form vertices of the hypercubetopology.
 9. The system of claim 1, wherein: each of the at least theportion of the dynamically configurable communication elements furthercomprise a plurality of output ports to which access is controlled bythe routing engine; and for a given one of the dynamically configurablecommunication elements, the routing engine of the given dynamicallyconfigurable communication element is configured to detect a collisionbetween multiple data items requesting access to a given one of theoutput ports and, in response to detecting the collision, the routingengine of the given dynamically configurable communication element isfurther configured to arbitrate which of the multiple data itemsreceives access to the given output port.
 10. The system of claim 1,wherein to transfer the data item through the intermediate subset of thedynamically configurable communication elements, the routing engines ofthe intermediate subset are configurable to route the data itemdependent upon an address associated with the destination device. 11.The system of claim 10, wherein the address is encoded as a relativeaddress or as a sequence of relative addresses.
 12. The system of claim1, wherein the at least some of the processors and the at least some ofthe dynamically configurable communication elements that are coupledtogether in the interspersed arrangement are configured as a pluralityof units, each unit including a respective processor and a respectivedynamically configurable communication element, wherein the units areuniquely addressable according to their positions within theinterspersed arrangement.
 13. The system of claim 12, wherein the unitsare uniquely addressable via a global serial bus.
 14. The system ofclaim 12, wherein a given one of the units is operable to convey a samedata item to each other one of at least a subset of the units.
 15. Thesystem of claim 14, wherein the given unit is operable to convey thesame data item to each other one of the at least a subset of the unitsusing a single operation.
 16. The system of claim 1, wherein a given oneof the processors is operable to cause data stored in a given one of thedynamically configurable communication elements to be read and conveyedto the given processor, wherein the given dynamically configurablecommunication element is coupled to the given processor through one ormore intervening ones of the dynamically configurable communicationelements.
 17. The system of claim 16, wherein to cause the data storedin the given dynamically configurable communication element to be readand conveyed to the given processor, the given processor is operable toaccess an address within a neighboring one of the one or moreintervening dynamically configurable communication elements.
 18. Thesystem of claim 17, wherein in response to access to the address by thegiven processor, the neighboring dynamically configurable communicationelement is operable to convey a read operation to the given dynamicallyconfigurable communication element.
 19. The system of claim 18, whereinin response to receiving the read operation, the given dynamicallyconfigurable communication element is operable to convey a writeoperation to the neighboring dynamically configurable communicationelement, wherein the write operation includes data to be returned to thegiven processor.
 20. The system of claim 1, wherein the source device isoperable to perform operations including read operations and writeoperations, wherein the operations include an address and data.
 21. Thesystem of claim 20, wherein read operations and write operations occurduring distinct phases of a clock signal.
 22. The system of claim 1,wherein one or more of the dynamically configurable communicationelements is programmable to route data according to different modes ofrouting operation.
 23. The system of claim 1, wherein one or more of theintermediate subset of dynamically configurable communication elementsis programmable to route data between the source device and thedestination device according to a selected one of several possible pathsbetween the source device and the destination device.
 24. The system ofclaim 23, wherein the one or more of the intermediate subset ofdynamically configurable communication elements is further programmablesuch that on different occasions, data routed between the source deviceand the destination device takes different ones of the several possiblepaths between the source device and the destination device.
 25. Thesystem of claim 1, wherein each of the members of the intermediatesubset includes a respective input register and a respective outputregister, wherein in response to receiving stalling information, a givenmember of the intermediate subset is configured to store distinct dataitems within its respective input register and output register.
 26. Thesystem of claim 25, wherein the distinct data items correspond todistinct data elements of a single data packet.
 27. The system of claim1, wherein at least some of the processors are operable to executeprogrammer-specified instructions, fixed functions, or hardwareacceleration operations.
 28. The system of claim 1, wherein each of therouting engines of the intermediate subset includes a respectiveconfiguration register, and wherein to transfer the data item throughthe intermediate subset of the dynamically configurable communicationelements, each routing engine of the intermediate subset is configurableto route the data item dependent on a state of its respectiveconfiguration register.
 29. The system of claim 28, wherein therespective configuration registers of the routing engines of theintermediate subset are programmable by one or more of: one or more ofthe processors; one or more of the dynamically configurablecommunication elements; one or more control words embedded with dataitems to be routed; or an interface with an independent side channelthat communicates with two or more DCC elements or processors.
 30. Thesystem of claim 28, wherein the respective configuration registers ofthe routing engines of the intermediate subset are programmable prior tothe routing engines of the intermediate subset receiving data items tobe routed.
 31. The system of claim 28, wherein the respectiveconfiguration registers of the routing engines of the intermediatesubset are programmable in response to control words received along withdata items to be routed.
 32. The system of claim 28, wherein therespective configuration registers of the routing engines of theintermediate subset are partly programmable prior to the routing enginesof the intermediate subset receiving data items to be routed and partlyprogrammable in response to control words received along with data itemsto be routed.
 33. The system of claim 1, wherein at least one of theprocessors is configured to obtain data from two or more of thedynamically configurable communication elements simultaneously.
 34. Thesystem of claim 1, wherein the memory of a given one of the dynamicallyconfigurable communication elements is shared among a given subset ofthe plurality of processors.
 35. The system of claim 1, whereindifferent pathways are operable to be created for data transfer amongdifferent subsets of the dynamically configurable communicationelements, wherein one or more of the different pathways are specifiedvia one or more data elements, each comprising a plurality of portions,wherein for a given one of the different pathways, each portionspecifies configuration information of the data transfer for arespective dynamically configurable communication element along thegiven pathway, wherein during data transfer each dynamicallyconfigurable communication element along the given pathway consumes itsrespective portion of the data element.
 36. The system of claim 1,wherein different pathways are operable to be created for data transferamong different subsets of the dynamically configurable communicationelements, wherein one or more of the different pathways are specifiedvia one or more data elements, each comprising a plurality of portions,wherein for a given one of the different pathways, each portionspecifies configuration information of the data transfer for arespective dynamically configurable communication element along thegiven pathway, wherein during data transfer each dynamicallyconfigurable communication element along the given pathway uses itsrespective portion of the data element without consuming its respectiveportion of the data element.
 37. The system of claim 1, wherein one ormore of the plurality of dynamically configurable communication elementsselectively operates in a synchronous data transfer mode or atransparent data transfer mode, wherein, when a given dynamicallyconfigurable communication element operates in the synchronous datatransfer mode, the given dynamically configurable communication elementoperates synchronously to a master clock, and wherein, when the givendynamically configurable communication element operates in thetransparent data transfer mode, at least a portion of the givendynamically configurable communication element operates without a clock.38. A method for operating a multiprocessor system, the methodcomprising: executing at least one program on a plurality of processors;wherein said executing comprises: at least a subset of the plurality ofprocessors communicating with each other through a plurality ofdynamically configurable communication elements, wherein each of atleast a portion of the dynamically configurable communication elementscomprises a memory and a routing engine, and wherein at least some ofthe processors and at least some of the dynamically configurablecommunication elements are coupled together in an interspersedarrangement; a source device initiating transfer of a data item throughan intermediate subset of the dynamically configurable communicationelements to a destination device; wherein the source device correspondsto a particular one of the processors, a particular one of thedynamically configurable communication elements, or an input/outputdevice; wherein the destination device corresponds to a different one ofthe processors, a different one of the dynamically configurablecommunication elements, or a different input/output device; in responseto detecting a stall after the source device begins transfer of the dataitem to the destination device and prior to receipt of all of the dataitem at the destination device, a stalling device propagating stallinginformation through one or more of the intermediate subset towards thesource device; in response to receiving the stalling information, atleast one of the intermediate subset buffering all or part of the dataitem.
 39. The method of claim 38, wherein executing the at least oneprogram further comprises executing a Fast Fourier Transform (FFT). 40.The method of claim 38, wherein executing the at least one programfurther comprises executing vector arithmetic.
 41. The method of claim38, wherein the stalling device includes the destination device or amember of the intermediate subset.
 42. The method of claim 38, whereinthe data item is one of several data elements of a data packet, andwherein the method further comprises the source device suspendingtransfer of the data packet in response to receiving the stallinginformation.
 43. The method of claim 38, wherein the at least some ofthe processors and the at least some of the dynamically configurablecommunication elements are physically stacked on a single integratedcircuit substrate such that the interspersed arrangement supports athree dimensional matrix.
 44. The method of claim 38, wherein the atleast some of the processors and the at least some of the dynamicallyconfigurable communication elements are distributed across two or moreintegrated circuit substrates.
 45. The method of claim 44, wherein thetwo or more integrated circuit substrates are bonded together.
 46. Themethod of claim 38, wherein two or more of the processors and two ormore of the dynamically configurable communication elements are coupledtogether to implement a hypercube topology, wherein the two or more ofthe dynamically configurable communication elements form vertices of thehypercube topology.
 47. The method of claim 38, wherein two or more ofthe processors and two or more of the dynamically configurablecommunication elements are coupled together to implement a hypercubetopology, wherein the two or more of the processors form vertices of thehypercube topology.
 48. The method of claim 38, wherein each of the atleast the portion of the dynamically configurable communication elementsfurther comprises a plurality of output ports to which access iscontrolled by the routing engine, wherein said executing furthercomprises: for a given one of the dynamically configurable communicationelements, the routing engine of the given dynamically configurablecommunication element detecting a collision between multiple data itemsrequesting access to a given one of the output ports; and in response todetecting the collision, the routing engine of the given dynamicallyconfigurable communication element arbitrating which of the multipledata items receives access to the given output port.
 49. The method ofclaim 38, wherein said executing further comprises the routing enginesof the intermediate subset routing the data item dependent upon anaddress associated with the destination device.
 50. The method of claim49, wherein the address is encoded as a relative address or as asequence of relative addresses.
 51. The method of claim 38, wherein eachof the routing engines of the intermediate subset includes a respectiveconfiguration register, and wherein said executing further compriseseach routing engine of the intermediate subset routing the data itemdependent on a state of its respective configuration register.
 52. Themethod of claim 51, wherein said executing further comprises programmingthe respective configuration registers of the routing engines of theintermediate subset, wherein the programming is performed by one or moreof: one or more of the processors; one or more of the dynamicallyconfigurable communication elements; one or more control words embeddedwith data items to be routed; or an interface with an independent sidechannel that communicates with two or more DCC elements or processors.53. The method of claim 51, wherein said executing further comprisesprogramming the respective configuration registers of the routingengines of the intermediate subset prior to the routing engines of theintermediate subset receiving data items to be routed.
 54. The method ofclaim 51, wherein said executing further comprises programming therespective configuration registers of the routing engines of theintermediate subset in response to control words received along withdata items to be routed.
 55. The method of claim 51, wherein saidexecuting further comprises partially programming the respectiveconfiguration registers of the routing engines of the intermediatesubset prior to the routing engines of the intermediate subset receivingdata items to be routed and partially programming the respectiveconfiguration registers of the routing engines of the intermediatesubset in response to control words received along with data items to berouted.
 56. The method of claim 38, wherein said executing furthercomprises at least one of the processors obtaining data from two or moreof the dynamically configurable communication elements simultaneously.57. The method of claim 38, wherein said executing further comprisessharing the memory of a given one of the dynamically configurablecommunication elements among a given subset of the plurality ofprocessors.
 58. The method of claim 38, wherein said executing furthercomprises creating different pathways for data transfer among differentsubsets of the dynamically configurable communication elements, whereinone or more of the different pathways are specified via one or more dataelements, each comprising a plurality of portions, wherein for a givenone of the different pathways, each portion specifies configurationinformation of the data transfer for a respective dynamicallyconfigurable communication element along the given pathway, whereinduring data transfer each dynamically configurable communication elementalong the given pathway consumes its respective portion of the dataelement.
 59. The method of claim 38, wherein said executing furthercomprises creating different pathways for data transfer among differentsubsets of the dynamically configurable communication elements, whereinone or more of the different pathways are specified via one or more dataelements, each comprising a plurality of portions, wherein for a givenone of the different pathways, each portion specifies configurationinformation of the data transfer for a respective dynamicallyconfigurable communication element along the given pathway, whereinduring data transfer each dynamically configurable communication elementalong the given pathway uses its respective portion of the data elementwithout consuming its respective portion of the data element.
 60. Themethod of claim 38, wherein said executing further comprises selectivelyconfiguring one or more of the plurality of dynamically configurablecommunication elements to operate in a synchronous data transfer mode ora transparent data transfer mode, wherein, when a given dynamicallyconfigurable communication element operates in the synchronous datatransfer mode, the given dynamically configurable communication elementoperates synchronously to a master clock, and wherein, when the givendynamically configurable communication element operates in thetransparent data transfer mode, at least a portion of the givendynamically configurable communication element operates without a clock.61. A method of manufacturing an integrated circuit, the methodcomprising: fabricating a unit comprising a processor and a dynamicallyconfigurable communication element, wherein the dynamically configurablecommunication element comprises a memory and a routing engine; andplacing and interconnecting a plurality of the units on a substrate,wherein processors and dynamically configurable communication elementsof at least some of the units are coupled together in an interspersedarrangement; wherein a source device is configurable to transfer a dataitem through an intermediate subset of the dynamically configurablecommunication elements to a destination device; wherein the sourcedevice corresponds to a particular one of the processors, a particularone of the dynamically configurable communication elements, or aninput/output device; wherein the destination device corresponds to adifferent one of the processors, a different one of the dynamicallyconfigurable communication elements, or a different input/output device;wherein, in response to detecting a stall after the source device beginstransfer of the data item to the destination device and prior to receiptof all of the data item at the destination device, a stalling device isoperable to propagate stalling information through one or more of theintermediate subset towards the source device; wherein in response toreceiving the stalling information, at least one of the intermediatesubset is operable to buffer all or part of the data item.
 62. Themethod of claim 61, wherein said placing and interconnecting comprisesphysically stacking at least some of the processors and at least some ofthe dynamically configurable communication elements on a singleintegrated circuit substrate such that the interspersed arrangementsupports a three dimensional matrix.
 63. The method of claim 61, furthercomprising placing and interconnecting a plurality of the units on adifferent substrate, such that the units are distributed across two ormore integrated circuit substrates.
 64. The method of claim 63, furthercomprising bonding the two or more integrated circuit substratestogether.
 65. The method of claim 61, wherein said placing andinterconnecting comprises coupling together at least a subset of theprocessors and at least a subset of the dynamically configurablecommunication elements in a hypercube topology, wherein members of theat least a subset of the dynamically configurable communication elementsform vertices of the hypercube topology.
 66. The method of claim 61,wherein said placing and interconnecting comprises coupling together atleast a subset of the processors and at least a subset of thedynamically configurable communication elements in a hypercube topology,wherein members of the at least a subset of the processors form verticesof the hypercube topology.